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-rw-r--r--c.html.markdown883
1 files changed, 441 insertions, 442 deletions
diff --git a/c.html.markdown b/c.html.markdown
index 22f251f2..8e170300 100644
--- a/c.html.markdown
+++ b/c.html.markdown
@@ -16,16 +16,16 @@ memory management and C will take you as far as you need to go.
```c
// Single-line comments start with // - only available in C99 and later.
-/*
+ /*
Multi-line comments look like this. They work in C89 as well.
-*/
+ */
-// Constants: #define <keyword>
+ // Constants: #define <keyword>
#define DAYS_IN_YEAR 365
-// Enumeration constants are also ways to declare constants.
-enum days {SUN = 1, MON, TUE, WED, THU, FRI, SAT};
-// MON gets 2 automatically, TUE gets 3, etc.
+ // Enumeration constants are also ways to declare constants.
+ enum days {SUN = 1, MON, TUE, WED, THU, FRI, SAT};
+// MON gets 2 automatically, TUE gets 3, etc.
// Import headers with #include
#include <stdlib.h>
@@ -34,388 +34,386 @@ enum days {SUN = 1, MON, TUE, WED, THU, FRI, SAT};
// (File names between <angle brackets> are headers from the C standard library.)
// For your own headers, use double quotes instead of angle brackets:
-#include "my_header.h"
+//#include "my_header.h"
// Declare function signatures in advance in a .h file, or at the top of
// your .c file.
-void function_1(char c);
+void function_1();
int function_2(void);
// Must declare a 'function prototype' before main() when functions occur after
// your main() function.
-int add_two_ints(int x1, int x2); // function prototype
+int add_two_ints(int x1, int x2); // function prototype
// Your program's entry point is a function called
// main with an integer return type.
int main() {
- // print output using printf, for "print formatted"
- // %d is an integer, \n is a newline
- printf("%d\n", 0); // => Prints 0
- // All statements must end with a semicolon
-
- ///////////////////////////////////////
- // Types
- ///////////////////////////////////////
-
- // ints are usually 4 bytes
- int x_int = 0;
-
- // shorts are usually 2 bytes
- short x_short = 0;
-
- // chars are guaranteed to be 1 byte
- char x_char = 0;
- char y_char = 'y'; // Char literals are quoted with ''
-
- // longs are often 4 to 8 bytes; long longs are guaranteed to be at least
- // 64 bits
- long x_long = 0;
- long long x_long_long = 0;
-
- // floats are usually 32-bit floating point numbers
- float x_float = 0.0;
-
- // doubles are usually 64-bit floating-point numbers
- double x_double = 0.0;
-
- // Integral types may be unsigned.
- unsigned short ux_short;
- unsigned int ux_int;
- unsigned long long ux_long_long;
-
- // chars inside single quotes are integers in machine's character set.
- '0' // => 48 in the ASCII character set.
- 'A' // => 65 in the ASCII character set.
-
- // sizeof(T) gives you the size of a variable with type T in bytes
- // sizeof(obj) yields the size of the expression (variable, literal, etc.).
- printf("%zu\n", sizeof(int)); // => 4 (on most machines with 4-byte words)
-
-
- // If the argument of the `sizeof` operator is an expression, then its argument
- // is not evaluated (except VLAs (see below)).
- // The value it yields in this case is a compile-time constant.
- int a = 1;
- // size_t is an unsigned integer type of at least 2 bytes used to represent
- // the size of an object.
- size_t size = sizeof(a++); // a++ is not evaluated
- printf("sizeof(a++) = %zu where a = %d\n", size, a);
- // prints "sizeof(a++) = 4 where a = 1" (on a 32-bit architecture)
-
- // Arrays must be initialized with a concrete size.
- char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
- int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
- // (assuming 4-byte words)
-
-
- // You can initialize an array to 0 thusly:
- char my_array[20] = {0};
-
- // Indexing an array is like other languages -- or,
- // rather, other languages are like C
- my_array[0]; // => 0
-
- // Arrays are mutable; it's just memory!
- my_array[1] = 2;
- printf("%d\n", my_array[1]); // => 2
-
- // In C99 (and as an optional feature in C11), variable-length arrays (VLAs)
- // can be declared as well. The size of such an array need not be a compile
- // time constant:
- printf("Enter the array size: "); // ask the user for an array size
- char buf[0x100];
- fgets(buf, sizeof buf, stdin);
-
- // strtoul parses a string to an unsigned integer
- size_t size = strtoul(buf, NULL, 10);
- int var_length_array[size]; // declare the VLA
- printf("sizeof array = %zu\n", sizeof var_length_array);
-
- // A possible outcome of this program may be:
- // > Enter the array size: 10
- // > sizeof array = 40
-
- // Strings are just arrays of chars terminated by a NULL (0x00) byte,
- // represented in strings as the special character '\0'.
- // (We don't have to include the NULL byte in string literals; the compiler
- // inserts it at the end of the array for us.)
- char a_string[20] = "This is a string";
- printf("%s\n", a_string); // %s formats a string
-
- printf("%d\n", a_string[16]); // => 0
- // i.e., byte #17 is 0 (as are 18, 19, and 20)
-
- // If we have characters between single quotes, that's a character literal.
- // It's of type `int`, and *not* `char` (for historical reasons).
- int cha = 'a'; // fine
- char chb = 'a'; // fine too (implicit conversion from int to char)
-
- //Multi-dimensional arrays:
- int multi_array[2][5] = {
- {1, 2, 3, 4, 5},
- {6, 7, 8, 9, 0}
- };
- //access elements:
- int array_int = multi_array[0][2]; // => 3
-
- ///////////////////////////////////////
- // Operators
- ///////////////////////////////////////
-
- // Shorthands for multiple declarations:
- int i1 = 1, i2 = 2;
- float f1 = 1.0, f2 = 2.0;
-
- int a, b, c;
- a = b = c = 0;
-
- // Arithmetic is straightforward
- i1 + i2; // => 3
- i2 - i1; // => 1
- i2 * i1; // => 2
- i1 / i2; // => 0 (0.5, but truncated towards 0)
-
- f1 / f2; // => 0.5, plus or minus epsilon
- // Floating-point numbers and calculations are not exact
-
- // Modulo is there as well
- 11 % 3; // => 2
-
- // Comparison operators are probably familiar, but
- // there is no Boolean type in c. We use ints instead.
- // (Or _Bool or bool in C99.)
- // 0 is false, anything else is true. (The comparison
- // operators always yield 0 or 1.)
- 3 == 2; // => 0 (false)
- 3 != 2; // => 1 (true)
- 3 > 2; // => 1
- 3 < 2; // => 0
- 2 <= 2; // => 1
- 2 >= 2; // => 1
-
- // C is not Python - comparisons don't chain.
- int a = 1;
- // WRONG:
- int between_0_and_2 = 0 < a < 2;
- // Correct:
- int between_0_and_2 = 0 < a && a < 2;
-
- // Logic works on ints
- !3; // => 0 (Logical not)
- !0; // => 1
- 1 && 1; // => 1 (Logical and)
- 0 && 1; // => 0
- 0 || 1; // => 1 (Logical or)
- 0 || 0; // => 0
-
- //Conditional expression ( ? : )
- int a = 5;
- int b = 10;
- int z;
- z = (a > b) ? a : b; // => 10 "if a > b return a, else return b."
-
- //Increment and decrement operators:
- char *s = "iLoveC";
- int j = 0;
- s[j++]; // => "i". Returns the j-th item of s THEN increments value of j.
- j = 0;
- s[++j]; // => "L". Increments value of j THEN returns j-th value of s.
- // same with j-- and --j
-
- // Bitwise operators!
- ~0x0F; // => 0xF0 (bitwise negation, "1's complement")
- 0x0F & 0xF0; // => 0x00 (bitwise AND)
- 0x0F | 0xF0; // => 0xFF (bitwise OR)
- 0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
- 0x01 << 1; // => 0x02 (bitwise left shift (by 1))
- 0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
-
- // Be careful when shifting signed integers - the following are undefined:
- // - shifting into the sign bit of a signed integer (int a = 1 << 32)
- // - left-shifting a negative number (int a = -1 << 2)
- // - shifting by an offset which is >= the width of the type of the LHS:
- // int a = 1 << 32; // UB if int is 32 bits wide
-
- ///////////////////////////////////////
- // Control Structures
- ///////////////////////////////////////
-
- if (0) {
- printf("I am never run\n");
- } else if (0) {
- printf("I am also never run\n");
- } else {
- printf("I print\n");
- }
-
- // While loops exist
- int ii = 0;
- while (ii < 10) { //ANY value not zero is true.
- printf("%d, ", ii++); // ii++ increments ii AFTER using its current value.
- } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
-
- printf("\n");
-
- int kk = 0;
- do {
- printf("%d, ", kk);
- } while (++kk < 10); // ++kk increments kk BEFORE using its current value.
- // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
-
- printf("\n");
-
- // For loops too
- int jj;
- for (jj=0; jj < 10; jj++) {
- printf("%d, ", jj);
- } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
-
- printf("\n");
-
- // *****NOTES*****:
- // Loops and Functions MUST have a body. If no body is needed:
- int i;
- for (i = 0; i <= 5; i++) {
- ; // use semicolon to act as the body (null statement)
- }
-
- // branching with multiple choices: switch()
- switch (some_integral_expression) {
- case 0: // labels need to be integral *constant* expressions
- do_stuff();
- break; // if you don't break, control flow falls over labels
- case 1:
- do_something_else();
- break;
- default:
- // if `some_integral_expression` didn't match any of the labels
- fputs("error!\n", stderr);
- exit(-1);
- break;
- }
-
-
- ///////////////////////////////////////
- // Typecasting
- ///////////////////////////////////////
-
- // Every value in C has a type, but you can cast one value into another type
- // if you want (with some constraints).
-
- int x_hex = 0x01; // You can assign vars with hex literals
-
- // Casting between types will attempt to preserve their numeric values
- printf("%d\n", x_hex); // => Prints 1
- printf("%d\n", (short) x_hex); // => Prints 1
- printf("%d\n", (char) x_hex); // => Prints 1
-
- // Types will overflow without warning
- printf("%d\n", (unsigned char) 257); // => 1 (Max char = 255 if char is 8 bits long)
-
- // For determining the max value of a `char`, a `signed char` and an `unsigned char`,
- // respectively, use the CHAR_MAX, SCHAR_MAX and UCHAR_MAX macros from <limits.h>
-
- // Integral types can be cast to floating-point types, and vice-versa.
- printf("%f\n", (float)100); // %f formats a float
- printf("%lf\n", (double)100); // %lf formats a double
- printf("%d\n", (char)100.0);
-
- ///////////////////////////////////////
- // Pointers
- ///////////////////////////////////////
-
- // A pointer is a variable declared to store a memory address. Its declaration will
- // also tell you the type of data it points to. You can retrieve the memory address
- // of your variables, then mess with them.
-
- int x = 0;
- printf("%p\n", (void *)&x); // Use & to retrieve the address of a variable
- // (%p formats an object pointer of type void *)
- // => Prints some address in memory;
-
-
- // Pointers start with * in their declaration
- int *px, not_a_pointer; // px is a pointer to an int
- px = &x; // Stores the address of x in px
- printf("%p\n", (void *)px); // => Prints some address in memory
- printf("%zu, %zu\n", sizeof(px), sizeof(not_a_pointer));
- // => Prints "8, 4" on a typical 64-bit system
-
- // To retrieve the value at the address a pointer is pointing to,
- // put * in front to dereference it.
- // Note: yes, it may be confusing that '*' is used for _both_ declaring a
- // pointer and dereferencing it.
- printf("%d\n", *px); // => Prints 0, the value of x
-
- // You can also change the value the pointer is pointing to.
- // We'll have to wrap the dereference in parenthesis because
- // ++ has a higher precedence than *.
- (*px)++; // Increment the value px is pointing to by 1
- printf("%d\n", *px); // => Prints 1
- printf("%d\n", x); // => Prints 1
-
- // Arrays are a good way to allocate a contiguous block of memory
- int x_array[20]; //declares array of size 20 (cannot change size)
- int xx;
- for (xx = 0; xx < 20; xx++) {
- x_array[xx] = 20 - xx;
- } // Initialize x_array to 20, 19, 18,... 2, 1
+ // print output using printf, for "print formatted"
+ // %d is an integer, \n is a newline
+ printf("%d\n", 0); // => Prints 0
+ // All statements must end with a semicolon
+
+ ///////////////////////////////////////
+ // Types
+ ///////////////////////////////////////
+
+ // ints are usually 4 bytes
+ int x_int = 0;
+
+ // shorts are usually 2 bytes
+ short x_short = 0;
+
+ // chars are guaranteed to be 1 byte
+ char x_char = 0;
+ char y_char = 'y'; // Char literals are quoted with ''
+
+ // longs are often 4 to 8 bytes; long longs are guaranteed to be at least
+ // 64 bits
+ long x_long = 0;
+ long long x_long_long = 0;
+
+ // floats are usually 32-bit floating point numbers
+ float x_float = 0.0;
+
+ // doubles are usually 64-bit floating-point numbers
+ double x_double = 0.0;
+
+ // Integral types may be unsigned.
+ unsigned short ux_short;
+ unsigned int ux_int;
+ unsigned long long ux_long_long;
+
+ // chars inside single quotes are integers in machine's character set.
+ '0'; // => 48 in the ASCII character set.
+ 'A'; // => 65 in the ASCII character set.
+
+ // sizeof(T) gives you the size of a variable with type T in bytes
+ // sizeof(obj) yields the size of the expression (variable, literal, etc.).
+ printf("%zu\n", sizeof(int)); // => 4 (on most machines with 4-byte words)
+
+
+ // If the argument of the `sizeof` operator is an expression, then its argument
+ // is not evaluated (except VLAs (see below)).
+ // The value it yields in this case is a compile-time constant.
+ int a = 1;
+ // size_t is an unsigned integer type of at least 2 bytes used to represent
+ // the size of an object.
+ size_t size = sizeof(a++); // a++ is not evaluated
+ printf("sizeof(a++) = %zu where a = %d\n", size, a);
+ // prints "sizeof(a++) = 4 where a = 1" (on a 32-bit architecture)
+
+ // Arrays must be initialized with a concrete size.
+ char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
+ int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
+ // (assuming 4-byte words)
+
+
+ // You can initialize an array to 0 thusly:
+ char my_array[20] = {0};
+
+ // Indexing an array is like other languages -- or,
+ // rather, other languages are like C
+ my_array[0]; // => 0
+
+ // Arrays are mutable; it's just memory!
+ my_array[1] = 2;
+ printf("%d\n", my_array[1]); // => 2
+
+ // In C99 (and as an optional feature in C11), variable-length arrays (VLAs)
+ // can be declared as well. The size of such an array need not be a compile
+ // time constant:
+ printf("Enter the array size: "); // ask the user for an array size
+ char buf[0x100];
+ fgets(buf, sizeof buf, stdin);
+
+ // strtoul parses a string to an unsigned integer
+ size_t size2 = strtoul(buf, NULL, 10);
+ int var_length_array[size2]; // declare the VLA
+ printf("sizeof array = %zu\n", sizeof var_length_array);
+
+ // A possible outcome of this program may be:
+ // > Enter the array size: 10
+ // > sizeof array = 40
+
+ // Strings are just arrays of chars terminated by a NULL (0x00) byte,
+ // represented in strings as the special character '\0'.
+ // (We don't have to include the NULL byte in string literals; the compiler
+ // inserts it at the end of the array for us.)
+ char a_string[20] = "This is a string";
+ printf("%s\n", a_string); // %s formats a string
+
+ printf("%d\n", a_string[16]); // => 0
+ // i.e., byte #17 is 0 (as are 18, 19, and 20)
+
+ // If we have characters between single quotes, that's a character literal.
+ // It's of type `int`, and *not* `char` (for historical reasons).
+ int cha = 'a'; // fine
+ char chb = 'a'; // fine too (implicit conversion from int to char)
+
+ //Multi-dimensional arrays:
+ int multi_array[2][5] = {
+ {1, 2, 3, 4, 5},
+ {6, 7, 8, 9, 0}
+ };
+ //access elements:
+ int array_int = multi_array[0][2]; // => 3
+
+ ///////////////////////////////////////
+ // Operators
+ ///////////////////////////////////////
+
+ // Shorthands for multiple declarations:
+ int i1 = 1, i2 = 2;
+ float f1 = 1.0, f2 = 2.0;
+
+ int b, c;
+ b = c = 0;
+
+ // Arithmetic is straightforward
+ i1 + i2; // => 3
+ i2 - i1; // => 1
+ i2 * i1; // => 2
+ i1 / i2; // => 0 (0.5, but truncated towards 0)
+
+ f1 / f2; // => 0.5, plus or minus epsilon
+ // Floating-point numbers and calculations are not exact
+
+ // Modulo is there as well
+ 11 % 3; // => 2
+
+ // Comparison operators are probably familiar, but
+ // there is no Boolean type in c. We use ints instead.
+ // (Or _Bool or bool in C99.)
+ // 0 is false, anything else is true. (The comparison
+ // operators always yield 0 or 1.)
+ 3 == 2; // => 0 (false)
+ 3 != 2; // => 1 (true)
+ 3 > 2; // => 1
+ 3 < 2; // => 0
+ 2 <= 2; // => 1
+ 2 >= 2; // => 1
+
+ // C is not Python - comparisons don't chain.
+ // WRONG:
+ //int between_0_and_2 = 0 < a < 2;
+ // Correct:
+ int between_0_and_2 = 0 < a && a < 2;
+
+ // Logic works on ints
+ !3; // => 0 (Logical not)
+ !0; // => 1
+ 1 && 1; // => 1 (Logical and)
+ 0 && 1; // => 0
+ 0 || 1; // => 1 (Logical or)
+ 0 || 0; // => 0
+
+ //Conditional expression ( ? : )
+ int e = 5;
+ int f = 10;
+ int z;
+ z = (a > b) ? a : b; // => 10 "if a > b return a, else return b."
+
+ //Increment and decrement operators:
+ char *s = "iLoveC";
+ int j = 0;
+ s[j++]; // => "i". Returns the j-th item of s THEN increments value of j.
+ j = 0;
+ s[++j]; // => "L". Increments value of j THEN returns j-th value of s.
+ // same with j-- and --j
+
+ // Bitwise operators!
+ ~0x0F; // => 0xF0 (bitwise negation, "1's complement")
+ 0x0F & 0xF0; // => 0x00 (bitwise AND)
+ 0x0F | 0xF0; // => 0xFF (bitwise OR)
+ 0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
+ 0x01 << 1; // => 0x02 (bitwise left shift (by 1))
+ 0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
+
+ // Be careful when shifting signed integers - the following are undefined:
+ // - shifting into the sign bit of a signed integer (int a = 1 << 32)
+ // - left-shifting a negative number (int a = -1 << 2)
+ // - shifting by an offset which is >= the width of the type of the LHS:
+ // int a = 1 << 32; // UB if int is 32 bits wide
+
+ ///////////////////////////////////////
+ // Control Structures
+ ///////////////////////////////////////
+
+ if (0) {
+ printf("I am never run\n");
+ } else if (0) {
+ printf("I am also never run\n");
+ } else {
+ printf("I print\n");
+ }
+
+ // While loops exist
+ int ii = 0;
+ while (ii < 10) { //ANY value not zero is true.
+ printf("%d, ", ii++); // ii++ increments ii AFTER using its current value.
+ } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+
+ printf("\n");
+
+ int kk = 0;
+ do {
+ printf("%d, ", kk);
+ } while (++kk < 10); // ++kk increments kk BEFORE using its current value.
+ // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+
+ printf("\n");
+
+ // For loops too
+ int jj;
+ for (jj=0; jj < 10; jj++) {
+ printf("%d, ", jj);
+ } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+
+ printf("\n");
+
+ // *****NOTES*****:
+ // Loops and Functions MUST have a body. If no body is needed:
+ int i;
+ for (i = 0; i <= 5; i++) {
+ ; // use semicolon to act as the body (null statement)
+ }
+
+ // branching with multiple choices: switch()
+ switch (a) {
+ case 0: // labels need to be integral *constant* expressions
+ printf("Hey, 'a' equals 0!\n");
+ break; // if you don't break, control flow falls over labels
+ case 1:
+ printf("Huh, 'a' equals 1!\n");
+ break;
+ default:
+ // if `some_integral_expression` didn't match any of the labels
+ fputs("error!\n", stderr);
+ exit(-1);
+ break;
+ }
+
+ ///////////////////////////////////////
+ // Typecasting
+ ///////////////////////////////////////
+
+ // Every value in C has a type, but you can cast one value into another type
+ // if you want (with some constraints).
+
+ int x_hex = 0x01; // You can assign vars with hex literals
+
+ // Casting between types will attempt to preserve their numeric values
+ printf("%d\n", x_hex); // => Prints 1
+ printf("%d\n", (short) x_hex); // => Prints 1
+ printf("%d\n", (char) x_hex); // => Prints 1
+
+ // Types will overflow without warning
+ printf("%d\n", (unsigned char) 257); // => 1 (Max char = 255 if char is 8 bits long)
+
+ // For determining the max value of a `char`, a `signed char` and an `unsigned char`,
+ // respectively, use the CHAR_MAX, SCHAR_MAX and UCHAR_MAX macros from <limits.h>
+
+ // Integral types can be cast to floating-point types, and vice-versa.
+ printf("%f\n", (float)100); // %f formats a float
+ printf("%lf\n", (double)100); // %lf formats a double
+ printf("%d\n", (char)100.0);
+
+ ///////////////////////////////////////
+ // Pointers
+ ///////////////////////////////////////
+
+ // A pointer is a variable declared to store a memory address. Its declaration will
+ // also tell you the type of data it points to. You can retrieve the memory address
+ // of your variables, then mess with them.
+
+ int x = 0;
+ printf("%p\n", (void *)&x); // Use & to retrieve the address of a variable
+ // (%p formats an object pointer of type void *)
+ // => Prints some address in memory;
+
+
+ // Pointers start with * in their declaration
+ int *px, not_a_pointer; // px is a pointer to an int
+ px = &x; // Stores the address of x in px
+ printf("%p\n", (void *)px); // => Prints some address in memory
+ printf("%zu, %zu\n", sizeof(px), sizeof(not_a_pointer));
+ // => Prints "8, 4" on a typical 64-bit system
+
+ // To retrieve the value at the address a pointer is pointing to,
+ // put * in front to dereference it.
+ // Note: yes, it may be confusing that '*' is used for _both_ declaring a
+ // pointer and dereferencing it.
+ printf("%d\n", *px); // => Prints 0, the value of x
+
+ // You can also change the value the pointer is pointing to.
+ // We'll have to wrap the dereference in parenthesis because
+ // ++ has a higher precedence than *.
+ (*px)++; // Increment the value px is pointing to by 1
+ printf("%d\n", *px); // => Prints 1
+ printf("%d\n", x); // => Prints 1
+
+ // Arrays are a good way to allocate a contiguous block of memory
+ int x_array[20]; //declares array of size 20 (cannot change size)
+ int xx;
+ for (xx = 0; xx < 20; xx++) {
+ x_array[xx] = 20 - xx;
+ } // Initialize x_array to 20, 19, 18,... 2, 1
// Declare a pointer of type int and initialize it to point to x_array
- int* x_ptr = x_array;
- // x_ptr now points to the first element in the array (the integer 20).
- // This works because arrays often decay into pointers to their first element.
- // For example, when an array is passed to a function or is assigned to a pointer,
- // it decays into (implicitly converted to) a pointer.
- // Exceptions: when the array is the argument of the `&` (address-of) operator:
- int arr[10];
- int (*ptr_to_arr)[10] = &arr; // &arr is NOT of type `int *`!
- // It's of type "pointer to array" (of ten `int`s).
- // or when the array is a string literal used for initializing a char array:
- char arr[] = "foobarbazquirk";
- // or when it's the argument of the `sizeof` or `alignof` operator:
- int arr[10];
- int *ptr = arr; // equivalent with int *ptr = &arr[0];
- printf("%zu, %zu\n", sizeof arr, sizeof ptr); // probably prints "40, 4" or "40, 8"
-
-
- // Pointers are incremented and decremented based on their type
- // (this is called pointer arithmetic)
- printf("%d\n", *(x_ptr + 1)); // => Prints 19
- printf("%d\n", x_array[1]); // => Prints 19
-
- // You can also dynamically allocate contiguous blocks of memory with the
- // standard library function malloc, which takes one argument of type size_t
- // representing the number of bytes to allocate (usually from the heap, although this
- // may not be true on e.g. embedded systems - the C standard says nothing about it).
- int *my_ptr = malloc(sizeof(*my_ptr) * 20);
- for (xx = 0; xx < 20; xx++) {
- *(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx
- } // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
+ int* x_ptr = x_array;
+ // x_ptr now points to the first element in the array (the integer 20).
+ // This works because arrays often decay into pointers to their first element.
+ // For example, when an array is passed to a function or is assigned to a pointer,
+ // it decays into (implicitly converted to) a pointer.
+ // Exceptions: when the array is the argument of the `&` (address-of) operator:
+ int arr[10];
+ int (*ptr_to_arr)[10] = &arr; // &arr is NOT of type `int *`!
+ // It's of type "pointer to array" (of ten `int`s).
+ // or when the array is a string literal used for initializing a char array:
+ char otherarr[] = "foobarbazquirk";
+ // or when it's the argument of the `sizeof` or `alignof` operator:
+ int arraythethird[10];
+ int *ptr = arraythethird; // equivalent with int *ptr = &arr[0];
+ printf("%zu, %zu\n", sizeof arraythethird, sizeof ptr); // probably prints "40, 4" or "40, 8"
+
+
+ // Pointers are incremented and decremented based on their type
+ // (this is called pointer arithmetic)
+ printf("%d\n", *(x_ptr + 1)); // => Prints 19
+ printf("%d\n", x_array[1]); // => Prints 19
+
+ // You can also dynamically allocate contiguous blocks of memory with the
+ // standard library function malloc, which takes one argument of type size_t
+ // representing the number of bytes to allocate (usually from the heap, although this
+ // may not be true on e.g. embedded systems - the C standard says nothing about it).
+ int *my_ptr = malloc(sizeof(*my_ptr) * 20);
+ for (xx = 0; xx < 20; xx++) {
+ *(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx
+ } // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
// Dereferencing memory that you haven't allocated gives
// "unpredictable results" - the program is said to invoke "undefined behavior"
- printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? It may even crash.
-
- // When you're done with a malloc'd block of memory, you need to free it,
- // or else no one else can use it until your program terminates
- // (this is called a "memory leak"):
- free(my_ptr);
-
- // Strings are arrays of char, but they are usually represented as a
- // pointer-to-char (which is a pointer to the first element of the array).
- // It's good practice to use `const char *' when referring to a string literal,
- // since string literals shall not be modified (i.e. "foo"[0] = 'a' is ILLEGAL.)
- const char *my_str = "This is my very own string literal";
- printf("%c\n", *my_str); // => 'T'
-
- // This is not the case if the string is an array
- // (potentially initialized with a string literal)
- // that resides in writable memory, as in:
- char foo[] = "foo";
- foo[0] = 'a'; // this is legal, foo now contains "aoo"
-
- function_1();
+ printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? It may even crash.
+
+ // When you're done with a malloc'd block of memory, you need to free it,
+ // or else no one else can use it until your program terminates
+ // (this is called a "memory leak"):
+ free(my_ptr);
+
+ // Strings are arrays of char, but they are usually represented as a
+ // pointer-to-char (which is a pointer to the first element of the array).
+ // It's good practice to use `const char *' when referring to a string literal,
+ // since string literals shall not be modified (i.e. "foo"[0] = 'a' is ILLEGAL.)
+ const char *my_str = "This is my very own string literal";
+ printf("%c\n", *my_str); // => 'T'
+
+ // This is not the case if the string is an array
+ // (potentially initialized with a string literal)
+ // that resides in writable memory, as in:
+ char foo[] = "foo";
+ foo[0] = 'a'; // this is legal, foo now contains "aoo"
+
+ function_1();
} // end main function
///////////////////////////////////////
@@ -427,16 +425,16 @@ int main() {
int add_two_ints(int x1, int x2)
{
- return x1 + x2; // Use return to return a value
+ return x1 + x2; // Use return to return a value
}
/*
-Functions are call by value. When a function is called, the arguments passed to
-the function are copies of the original arguments (except arrays). Anything you
-do to the arguments in the function do not change the value of the original
-argument where the function was called.
+Functions are call by value. When a function is called, the arguments passed to
+≈the function are copies of the original arguments (except arrays). Anything you
+do to the arguments in the function do not change the value of the original
+argument where the function was called.
-Use pointers if you need to edit the original argument values.
+Use pointers if you need to edit the original argument values.
Example: in-place string reversal
*/
@@ -444,14 +442,14 @@ Example: in-place string reversal
// A void function returns no value
void str_reverse(char *str_in)
{
- char tmp;
- int ii = 0;
- size_t len = strlen(str_in); // `strlen()` is part of the c standard library
- for (ii = 0; ii < len / 2; ii++) {
- tmp = str_in[ii];
- str_in[ii] = str_in[len - ii - 1]; // ii-th char from end
- str_in[len - ii - 1] = tmp;
- }
+ char tmp;
+ int ii = 0;
+ size_t len = strlen(str_in); // `strlen()` is part of the c standard library
+ for (ii = 0; ii < len / 2; ii++) {
+ tmp = str_in[ii];
+ str_in[ii] = str_in[len - ii - 1]; // ii-th char from end
+ str_in[len - ii - 1] = tmp;
+ }
}
/*
@@ -463,13 +461,13 @@ printf("%s\n", c); // => ".tset a si sihT"
//if referring to external variables outside function, must use extern keyword.
int i = 0;
void testFunc() {
- extern int i; //i here is now using external variable i
+ extern int i; //i here is now using external variable i
}
//make external variables private to source file with static:
-static int i = 0; //other files using testFunc() cannot access variable i
-void testFunc() {
- extern int i;
+static int j = 0; //other files using testFunc() cannot access variable i
+void testFunc2() {
+ extern int j;
}
//**You may also declare functions as static to make them private**
@@ -486,8 +484,8 @@ my_type my_type_var = 0;
// Structs are just collections of data, the members are allocated sequentially,
// in the order they are written:
struct rectangle {
- int width;
- int height;
+ int width;
+ int height;
};
// It's not generally true that
@@ -497,20 +495,20 @@ struct rectangle {
void function_1()
{
- struct rectangle my_rec;
+ struct rectangle my_rec;
- // Access struct members with .
- my_rec.width = 10;
- my_rec.height = 20;
+ // Access struct members with .
+ my_rec.width = 10;
+ my_rec.height = 20;
- // You can declare pointers to structs
- struct rectangle *my_rec_ptr = &my_rec;
+ // You can declare pointers to structs
+ struct rectangle *my_rec_ptr = &my_rec;
- // Use dereferencing to set struct pointer members...
- (*my_rec_ptr).width = 30;
+ // Use dereferencing to set struct pointer members...
+ (*my_rec_ptr).width = 30;
- // ... or even better: prefer the -> shorthand for the sake of readability
- my_rec_ptr->height = 10; // Same as (*my_rec_ptr).height = 10;
+ // ... or even better: prefer the -> shorthand for the sake of readability
+ my_rec_ptr->height = 10; // Same as (*my_rec_ptr).height = 10;
}
// You can apply a typedef to a struct for convenience
@@ -518,34 +516,34 @@ typedef struct rectangle rect;
int area(rect r)
{
- return r.width * r.height;
+ return r.width * r.height;
}
// if you have large structs, you can pass them "by pointer" to avoid copying
// the whole struct:
-int area(const rect *r)
+int areaptr(const rect *r)
{
- return r->width * r->height;
+ return r->width * r->height;
}
///////////////////////////////////////
-// Function pointers
+// Function pointers
///////////////////////////////////////
/*
At run time, functions are located at known memory addresses. Function pointers are
-much like any other pointer (they just store a memory address), but can be used
+much like any other pointer (they just store a memory address), but can be used
to invoke functions directly, and to pass handlers (or callback functions) around.
However, definition syntax may be initially confusing.
Example: use str_reverse from a pointer
*/
void str_reverse_through_pointer(char *str_in) {
- // Define a function pointer variable, named f.
- void (*f)(char *); // Signature should exactly match the target function.
- f = &str_reverse; // Assign the address for the actual function (determined at run time)
- // f = str_reverse; would work as well - functions decay into pointers, similar to arrays
- (*f)(str_in); // Just calling the function through the pointer
- // f(str_in); // That's an alternative but equally valid syntax for calling it.
+ // Define a function pointer variable, named f.
+ void (*f)(char *); // Signature should exactly match the target function.
+ f = &str_reverse; // Assign the address for the actual function (determined at run time)
+ // f = str_reverse; would work as well - functions decay into pointers, similar to arrays
+ (*f)(str_in); // Just calling the function through the pointer
+ // f(str_in); // That's an alternative but equally valid syntax for calling it.
}
/*
@@ -557,39 +555,40 @@ typedef void (*my_fnp_type)(char *);
// Then used when declaring the actual pointer variable:
// ...
-// my_fnp_type f;
+// my_fnp_type f;
//Special characters:
-'\a' // alert (bell) character
-'\n' // newline character
-'\t' // tab character (left justifies text)
-'\v' // vertical tab
-'\f' // new page (form feed)
-'\r' // carriage return
-'\b' // backspace character
-'\0' // NULL character. Usually put at end of strings in C.
- // hello\n\0. \0 used by convention to mark end of string.
-'\\' // backslash
-'\?' // question mark
-'\'' // single quote
-'\"' // double quote
-'\xhh' // hexadecimal number. Example: '\xb' = vertical tab character
-'\ooo' // octal number. Example: '\013' = vertical tab character
+/*
+'\a'; // alert (bell) character
+'\n'; // newline character
+'\t'; // tab character (left justifies text)
+'\v'; // vertical tab
+'\f'; // new page (form feed)
+'\r'; // carriage return
+'\b'; // backspace character
+'\0'; // NULL character. Usually put at end of strings in C.
+// hello\n\0. \0 used by convention to mark end of string.
+'\\'; // backslash
+'\?'; // question mark
+'\''; // single quote
+'\"'; // double quote
+'\xhh'; // hexadecimal number. Example: '\xb' = vertical tab character
+'\ooo'; // octal number. Example: '\013' = vertical tab character
//print formatting:
-"%d" // integer
-"%3d" // integer with minimum of length 3 digits (right justifies text)
-"%s" // string
-"%f" // float
-"%ld" // long
-"%3.2f" // minimum 3 digits left and 2 digits right decimal float
-"%7.4s" // (can do with strings too)
-"%c" // char
-"%p" // pointer
-"%x" // hexadecimal
-"%o" // octal
-"%%" // prints %
-
+"%d"; // integer
+"%3d"; // integer with minimum of length 3 digits (right justifies text)
+"%s"; // string
+"%f"; // float
+"%ld"; // long
+"%3.2f"; // minimum 3 digits left and 2 digits right decimal float
+"%7.4s"; // (can do with strings too)
+"%c"; // char
+"%p"; // pointer
+"%x"; // hexadecimal
+"%o"; // octal
+"%%"; // prints %
+*/
///////////////////////////////////////
// Order of Evaluation
///////////////////////////////////////