Merge 0c5eb762c4 into 8e94abc88b

c.html.markdown

@@ -11,6 +11,7 @@ contributors:
   - ["Joshua Li", "https://github.com/JoshuaRLi"]
   - ["Dragos B. Chirila", "https://github.com/dchirila"]
   - ["Heitor P. de Bittencourt", "https://github.com/heitorPB/"]
+  - ["Chris Harding", "https://github.com/sjrct"]
 ---
 
 Ah, C. Still **the** language of modern high-performance computing.
@@ -27,7 +28,8 @@ memory management and C will take you as far as you need to go.
 >
 > `-Wall -Wextra -Werror -O2 -std=c99 -pedantic`
 >
-> For information on what these flags do as well as other flags, consult the man page for your C compiler (e.g. `man 1 gcc`) or just search online.
+> For information on what these flags do as well as other flags, consult the man
+> page for your C compiler (e.g. `man 1 gcc`) or just search online.
 
 ```c
 // Single-line comments start with // - only available in C99 and later.
@@ -68,21 +70,23 @@ enum days {SUN = 1, MON, TUE, WED = 99, THU, FRI, SAT};
 
 // Declare function signatures in advance in a .h file, or at the top of
 // your .c file.
-void function_1();
+void function_1(void);
-int function_2(void);
+int function_2(int a, float b);
 
-// At a minimum, you must declare a 'function prototype' before its use in any function.
+// At a minimum, you must declare a 'function prototype' before its use in any
-// Normally, prototypes are placed at the top of a file before any function definition.
+// function. Normally, prototypes are placed at the top of a file before any
+// function definition.
 int add_two_ints(int x1, int x2); // function prototype
-// although `int add_two_ints(int, int);` is also valid (no need to name the args),
+// although `int add_two_ints(int, int);` is also valid (no need to name the
-// it is recommended to name arguments in the prototype as well for easier inspection
+// args), it is recommended to name arguments in the prototype as well for
+// easier inspection
 
 // Function prototypes are not necessary if the function definition comes before
-// any other function that calls that function. However, it's standard practice to
+// any other function that calls that function. However, it's standard practice
-// always add the function prototype to a header file (*.h) and then #include that
+// to always add the function prototype to a header file (*.h) and then #include
-// file at the top. This prevents any issues where a function might be called
+// that file at the top. This prevents any issues where a function might be
-// before the compiler knows of its existence, while also giving the developer a
+// called before the compiler knows of its existence, while also giving the
-// clean header file to share with the rest of the project.
+// developer a clean header file to share with the rest of the project.
 
 // Your program's entry point is a function called "main". The return type can
 // be anything, however most operating systems expect a return type of `int` for
@@ -125,7 +129,8 @@ int main (int argc, char** argv)
   short x_short = 0;
 
   // chars are defined as the smallest addressable unit for a processor.
-  // This is usually 1 byte, but for some systems it can be more (ex. for TMS320 from TI it's 2 bytes).
+  // This is usually 1 byte, but for some systems it can be more
+  // (ex. for TMS320 from TI it's 2 bytes).
   char x_char = 0;
   char y_char = 'y'; // Char literals are quoted with ''
 
@@ -153,8 +158,8 @@ int main (int argc, char** argv)
   // 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
+  // If the argument of the `sizeof` operator is an expression, then its
-  // is not evaluated (except VLAs (see below)).
+  // 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
@@ -171,15 +176,15 @@ int main (int argc, char** argv)
   // You can initialize an array of twenty ints that all equal 0 thusly:
   int my_array[20] = {0};
   // where the "{0}" part is called an "array initializer".
-  // All elements (if any) past the ones in the initializer are initialized to 0:
+  // Elements (if any) past the ones in the initializer are initialized to 0:
   int my_array[5] = {1, 2};
   // So my_array now has five elements, all but the first two of which are 0:
   // [1, 2, 0, 0, 0]
-  // NOTE that you get away without explicitly declaring the size
+  // NOTE that you get away without explicitly declaring the size of the
-  // of the array IF you initialize the array on the same line:
+  // array IF you initialize the array on the same line:
   int my_array[] = {0};
-  // NOTE that, when not declaring the size, the size of the array is the number
+  // NOTE that, when not declaring the size, the array's size is the number of
-  // of elements in the initializer. With "{0}", my_array is now of size one: [0]
+  // elements in the initializer. With "{0}", my_array is now of size one: [0]
   // To evaluate the size of the array at run-time, divide its byte size by the
   // byte size of its element type:
   size_t my_array_size = sizeof(my_array) / sizeof(my_array[0]);
@@ -249,7 +254,7 @@ int main (int argc, char** argv)
   i2 * i1; // => 2
   i1 / i2; // => 0 (0.5, but truncated towards 0)
 
-  // You need to cast at least one integer to float to get a floating-point result
+  // You need to cast at least one int to float to get a floating-point result
   (float)i1 / i2; // => 0.5f
   i1 / (double)i2; // => 0.5 // Same with double
   f1 / f2; // => 0.5, plus or minus epsilon
@@ -366,13 +371,17 @@ int main (int argc, char** argv)
   printf("\n");
 
   // *****NOTES*****:
-  // Loops and Functions MUST have a body. If no body is needed:
+  // If the body of control expression is only one statement then parentheses
+  // are optional, but recommended:
+  for (jj = 0; jj < 5; jj++)
+      printf("%d\n", jj);
+
+  // Loops and if statements 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)
   }
   // Or
-  for (i = 0; i <= 5; i++);
+  for (i = 0; i <= 5; i++); // semicolon acts as the body (null statement)
 
   // branching with multiple choices: switch()
   switch (a) {
@@ -441,8 +450,9 @@ int main (int argc, char** argv)
   // 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`,
+  // For determining the max value of a `char`, a `signed char` and an
-  // respectively, use the CHAR_MAX, SCHAR_MAX and UCHAR_MAX macros from <limits.h>
+  // `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", (double) 100); // %f always formats a double...
@@ -453,9 +463,9 @@ int main (int argc, char** argv)
   // Pointers
   ///////////////////////////////////////
 
-  // A pointer is a variable declared to store a memory address. Its declaration will
+  // A pointer is a variable declared to store a memory address. Its declaration
-  // also tell you the type of data it points to. You can retrieve the memory address
+  // will also tell you the type of data it points to. You can retrieve the
-  // of your variables, then mess with them.
+  // 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
@@ -493,9 +503,9 @@ int main (int argc, char** argv)
   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,
+  // For example, when an array is passed to a function or is assigned to a
-  // it decays into (implicitly converted to) a pointer.
+  // pointer, it decays into (implicitly converted to) a pointer.
-  // Exceptions: when the array is the argument of the `&` (address-of) operator:
+  // Exception: 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).
@@ -514,22 +524,23 @@ int main (int argc, char** argv)
 
   // 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
+  // representing the number of bytes to allocate (usually from the heap,
-  // may not be true on e.g. embedded systems - the C standard says nothing about it).
+  // 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)
 
-  // Be careful passing user-provided values to malloc! If you want
+  // Be careful passing user-provided values to malloc! If you want to be safe,
-  // to be safe, you can use calloc instead (which, unlike malloc, also zeros out the memory)
+  // you can use calloc instead (which, unlike malloc, also zeros the memory)
   int* my_other_ptr = calloc(20, sizeof(int));
 
-  // Note that there is no standard way to get the length of a
+  // Note that there is no standard way to get the length of a dynamically
-  // dynamically allocated array in C. Because of this, if your arrays are
+  // allocated array in C. Because of this, if your arrays are going to be
-  // going to be passed around your program a lot, you need another variable
+  // passed around your program a lot, you need another variable to keep track
-  // to keep track of the number of elements (size) of an array. See the
+  // of the number of elements (size) of an array. See the functions section
-  // functions section for more info.
+  // for more info.
   size_t size = 10;
   int *my_arr = calloc(size, sizeof(int));
   // Add an element to the array
@@ -541,9 +552,9 @@ int main (int argc, char** argv)
   }
   my_arr[10] = 5;
 
-  // Dereferencing memory that you haven't allocated gives
+  // Dereferencing memory that you haven't allocated gives "unpredictable
-  // "unpredictable results" - the program is said to invoke "undefined behavior"
+  // results" - the program is said to invoke "undefined behavior"
-  printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? It may even crash.
+  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
@@ -552,8 +563,8 @@ int main (int argc, char** argv)
 
   // 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,
+  // 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.)
+  // 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'
 
@@ -635,8 +646,8 @@ printf("first: %d\nsecond: %d\n", first, second);
 // Return multiple values.
 // C does not allow for returning multiple values with the return statement. If
 // you would like to return multiple values, then the caller must pass in the
-// variables where they would like the returned values to go. These variables must
+// variables where they would like the returned values to go. These variables
-// be passed in as pointers such that the function can modify them.
+// must be passed in as pointers such that the function can modify them.
 int return_multiple(int *array_of_3, int *ret1, int *ret2, int *ret3)
 {
     if (array_of_3 == NULL)
@@ -672,15 +683,15 @@ printIntArray(my_arr, size);
 // will print "arr[0] is: 1" etc
 */
 
-// if referring to external variables outside function, you should use the extern keyword.
+// if referring to external variables outside function, use the extern keyword.
 int i = 0;
-void testFunc() {
+void testFunc(void) {
   extern int i; //i here is now using external variable i
 }
 
 // make external variables private to source file with static:
 static int j = 0; //other files using testFunc2() cannot access variable j
-void testFunc2() {
+void testFunc2(void) {
   extern int j;
 }
 // The static keyword makes a variable inaccessible to code outside the
@@ -693,6 +704,18 @@ void testFunc2() {
 // declared with some other starting value.
 //**You may also declare functions as static to make them private**
 
+// Note that before C23, and unlike C++, functions taking no arguments without
+// an explicit `void` inside the parameter list will be treated as taking an
+// unknown number of arguments rather than no arguments.
+void testFunc3(void) {
+  // Functions can be prototyped inside other functions
+  void foobie();
+  void bletch(void);
+
+  foobie(1, 2, 3); // This will give a warning at most, not an error
+  bletch(1, 2, 3); // This will produce an error
+}
+
 ///////////////////////////////////////
 // User-defined types and structs
 ///////////////////////////////////////
@@ -713,10 +736,16 @@ struct rectangle {
 // due to potential padding between the structure members (this is for alignment
 // reasons). [1]
 
-void function_1()
+void function_1(void)
 {
   struct rectangle my_rec = { 1, 2 }; // Fields can be initialized immediately
 
+  // Fields can also be initialized in an arbitrary order with the field name
+  struct rectangle my_rec2 = {
+      .height = 2,
+      .width = 1
+  };
+
   // Access struct members with .
   my_rec.width = 10;
   my_rec.height = 20;
@@ -760,10 +789,10 @@ int areaptr(const rect *r)
 // Function pointers
 ///////////////////////////////////////
 /*
-At run time, functions are located at known memory addresses. Function pointers are
+At run time, functions are located at known memory addresses. Function pointers
-much like any other pointer (they just store a memory address), but can be used
+are much like any other pointer (they just store a memory address), but can be
-to invoke functions directly, and to pass handlers (or callback functions) around.
+used to invoke functions directly, and to pass handlers (or callback functions)
-However, definition syntax may be initially confusing.
+around. However, definition syntax may be initially confusing.
 
 Example: use str_reverse from a pointer
 */
@@ -773,12 +802,13 @@ void str_reverse_through_pointer(char *str_in) {
   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.
+  // f(str_in); // That's an alternative but equally valid syntax for calling it
 }
 
 /*
-As long as function signatures match, you can assign any function to the same pointer.
+As long as function signatures match, you can assign any function to the same
-Function pointers are usually typedef'd for simplicity and readability, as follows:
+pointer. Function pointers are usually typedef'd for simplicity and readability,
+as follows:
 */
 
 typedef void (*my_fnp_type)(char *);
@@ -864,8 +894,8 @@ as the C file.
 */
 
 /* A safe guard to prevent the header from being defined too many times. This */
-/* happens in the case of circle dependency, the contents of the header is    */
+/* happens in the case of circlular dependencies, or such as when a header is */
-/* already defined.                                                           */
+/* included alongside a header that includes the same header itself.          */
 #ifndef EXAMPLE_H /* if EXAMPLE_H is not yet defined. */
 #define EXAMPLE_H /* Define the macro EXAMPLE_H. */
 
@@ -897,7 +927,8 @@ enum traffic_light_state {GREEN, YELLOW, RED};
 
 /* Function prototypes can also be defined here for use in multiple files,   */
 /* but it is bad practice to define the function in the header. Definitions  */
-/* should instead be put in a C file.                                       */
+/* should instead be put in a C file. An uncommon exception is when defining */
+/* static inline functions.                                                  */
 Node createLinkedList(int *vals, int len);
 
 /* Beyond the above elements, other definitions should be left to a C source */