The <stdlib.h> header file declares four types and several functions of general use, and defines several macros. The functions perform string conversion, random number generation, searching and sorting, memory management, and similar tasks.

Types

size_t

• An unsigned integral type of the result of the sizeof operator.

wchar_t

• An integral type whose range of values can represent distinct codes for all members of the largest extended character set specified among the supported locales.

div_t

• A structure type that is the type of the value returned by the div function.

ldiv_t

• A structure type that is the type of the value returned by the ldiv function.

Macros

NULL

• Expands to an implementation-defined null pointer constant.

EXIT_FAILURE/EXIT_SUCCESS

• Expand to integral expressions for use as the argument to the exit function to return unsuccessful or successful termination status, respectively, to the host environment. These macros are useful as return values from the main function as well.

RAND_MAX

• Expands to an integral constant expression whose value is the maximum value returned by the rand function.

MB_CUR_MAX

• Expands to a positive integer expression whose value is the maximum number of bytes in a multibyte character for the extended character set specified by the current locale (category LC_TYPE), and whose value is never greater than MB_LEN_MAX.

String Conversion Functions

double atof(const char*nptr);

• Converts the string pointed to by nptr to double representation and returns the converted value. Except for its behavior when an error occurs, this function is equivalent to:

  strtod(nptr, (char **)NULL)

int atoi(const char*nptr);

• Converts the string pointed to by nptr to int representation and returns the converted value. Except for its behavior when an error occurs, this function is equivalent to:

  (int)strtol(nptr, (char **)NULL, 10)

long int atol(const char*nptr);

• Converts the string pointed to by nptr to long int representation and returns the converted value. Except for its behavior when an error occurs, this function is equivalent to:

  strtol(nptr, (char **)NULL, 10)

double strtod(const char*nptr, char **endptr);

• Converts the string pointed to by nptr to double representation.
  See your DEC C library routine documentation for a detailed description of this function.

long int strtol(const char*nptr, char **endptr, int base);

• Converts the string pointed to by nptr to long int representation.
  See your DEC C library routine documentation for a detailed description of this function.

unsigned long int strtoul(const char *nptr, char **endptr, int base);

• Converts the string pointed to by nptr to unsigned long int representation.
  See your DEC C library routine documentation for a detailed description of this function.

Pseudo-Random Sequence Generation Functions

int rand(void);

• Returns a sequence of pseudo-random integers in the range 0 to RAND_MAX.

void srand(unsigned intseed);

• Uses the argument as a seed for a new sequence of pseudo-random integers to be returned by subsequent calls to rand. If srand is then called with the same seed value, the sequence of pseudo-random integers is repeated. If rand is called before any calls to srand are made, the sequence generated is the same as when srand is first called with a seed value of 1. The srand function returns no value.

Memory Management Functions

void*calloc(size_t nmemb, size_t size);

• Allocates an area in memory for an array of nmemb items, each with size size. The area is initialized to all bits 0. The calloc function returns either a null pointer if unable to allocate, or a pointer to the allocated area.

void free(void*ptr);

• Deallocates the memory area pointed to by ptr that was allocated by a previous calloc, malloc, or realloc. If ptr is null, no action occurs. No value is returned.

void*malloc(size_t size);

• Allocates a contiguous area in memory for an object of size size. The area is not initialized. This function returns a pointer to the allocated area, or it returns a null pointer if unable to allocate.

void*realloc(void *ptr, size_t size);

• Changes the size of the area pointed to by ptr to the number of bytes specified by size. If ptr is null, the behavior of realloc is identical to malloc. The contents of the area are unchanged up to the lesser of the old and new sizes. This function returns either a null pointer if unable to resize, or a pointer to the possibly moved reallocated area.

Communication with the Environment

void abort(void);

• Causes abnormal program termination to occur, unless the SIGABRT signal is being caught and the signal handler does not return. The abort function cannot return to its caller.

int atexit(void (*func)(void));

• Registers the function pointed to by func to be called without arguments at normal program termination. Up to 32 functions can be registered. The atexit function returns 0 if the registration succeeds; otherwise, it returns nonzero.

void exit(intstatus);

• Causes normal program termination to occur. If a program executes more than one call to exit, the behavior is undefined. Upon execution, the following occurs:
  1. All functions registered by atexit are called in the reverse order of their registration.
  2. All open output streams are flushed, all open streams are closed, and all files created by tmpfile are removed.
  3. Control is returned to the host environment. The value of status corresponds to an errno value:
     • If the value status is 0 or EXIT_SUCCESS, a successful termination status is returned.
     • If the value status is EXIT_FAILURE, an unsuccessful termination status is returned.
     • Otherwise, an unsuccessful termination status is returned.

char*getenv(const char *name);

• Searches an environment list provided by the host environment.
  See your DEC C library routine documentation for a detailed description of this function.

int*system(const char *string);

• Passes the string pointed to by string to the host environment for execution by a command processor. A null pointer can be specified to inquire whether a command processor exists. If the argument is a null pointer, the system function returns nonzero if a command processor is available or 0 if one is not available. If the argument is not a null pointer, the return value is the status returned by the command processor or 0 if a command processor is not available.
  See your DEC C library routine documentation for a detailed description of this function.

Searching and Sorting Utilities

void *bsearch(const void *key, const void *base, size_t nmemb, size_t size, int (*compar) (const void *, const void *));

• Searches an array of nmemb objects for an element that matches the object pointed to by key. The first element of the array is pointed to by base; the size of each element is specified by size.
  You must first sort the array in ascending order according to the function pointed to by compar. The bsearch function calls the specified comparison function pointed to by compar with two arguments that point to the objects being compared (the key object and an array element). The comparison function returns:
  • An integer less than 0, if the first argument is less than the second argument
  • An integer greater than 0, if the first argument is greater than the second argument
  • An integer equal to 0, if the first argument equals the second argument
  
  The bsearch function returns a pointer to the matching element of the array, or a null pointer if no match is found.

void qsort(void *base, size_t nmemb, size_t size, int (*compar) (const void *, const void *));

• Sorts an array of nmemb objects in place. The first element of the array is pointed to by base; the size of each element is specified by size.
  The contents of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared. The comparison function returns:
  • An integer less than 0, if the first argument is less than the second argument
  • An integer greater than 0, if the first argument is greater than the second argument
  • An integer equal to 0, if the first argument equals the second argument
  
  If two compared elements are equal, their order in the sorted array is unspecified.
  The qsort function returns no value.

Integer Arithmetic Functions

int abs(intj);

• Returns the absolute value of an integer j.

div_t div(int numer, int denom);

• Computes the quotient and remainder of the division of numer by denom. The div function returns a structure of type div_t containing the quotient and remainder:

  int quot; /* quotient */ int rem; /* remainder */

long int labs(long intj);

• Returns the absolute value of a long integer j.

ldiv_t ldiv(long int numer, long int denom);

• Similar to the div function, except that the arguments and the members of the returned structure (which has type ldiv_t) all have type long int.

Multibyte Character Functions

int mblen(const char*s, size_t n);

• If s is not a null pointer, mblen determines the number of bytes comprising the multibyte character pointed to by s. The mblen function is equivalent to the following, except that the shift state of the mbtowc is not affected:

  mbtowc((wchar_t *)0, s, n);

  
  If s is a null pointer, the mblen function returns a nonzero value if multibyte character encodings have state-dependent encodings, and 0 if they do not.
  If s is not a null pointer, the mblen function returns one of the following values:

  • 0, if s points to the null character
  • The number of bytes that comprise the multibyte character, if the next n or fewer bytes form a valid multibyte character
  • --1, if they do not form a valid multibyte character

int mbtowc(wchar_t *pwc, const char *s, size_t n);

• If s is not a null pointer, mbtowc determines the number of bytes comprising the multibyte character pointed to by s. It then determines the code for the value of type wchar_t that corresponds to that multibyte character. (The value of the code corresponding to the null character is 0.) If the multibyte character is valid and pwc is not a null pointer, mbtowc stores the code in the object pointed to by pwc. At most, n bytes of the array pointed to by s are examined.
  If s is a null pointer, the mbtowc function returns a nonzero value if multibyte character encodings have state-dependent encodings, and 0 if they do not.
  If s is not a null pointer, the mbtowc function returns one of the following values:
  • 0, if s points to the null character
  • The number of bytes that comprise the converted multibyte character, if the next n or fewer bytes form a valid multibyte character
  • --1, if they do not form a valid multibyte character

int wctomb(char*s, wchar_t wchar);

• Determines the number of bytes needed to represent the multibyte character corresponding to the code whose value is wchar, including any change in shift state. This function then stores the multibyte character representation in the array object pointed to by s, if s is not a null pointer. At most, MB_CUR_MAX characters are stored. If the value of wchar is 0, the wctomb function is left in the initial shift state.
  If s is a null pointer, the wctomb function returns a nonzero value if multibyte character encodings have state-dependent encodings, and 0 if they do not.
  If s is not a null pointer, the wctomb function returns one of the following values:
  • --1, if the value of wchar does not correspond to a valid multibyte character
  • the number of bytes that comprise the multibyte character corresponding to the value of wchar

Multibyte String Functions

size_t mbstowcs(wchar_t *pwcs, const char *s, size_t n);

• Converts a sequence of multibyte characters that begin in the initial shift state from the array pointed to by s into a sequence of corresponding codes, and stores not more than n codes into the array pointed to by pwcs. A null character is converted to a code value of zero. No multibyte characters that follow a null character are examined or converted. Each multibyte character is converted as if by a call to mbtowc, except that the shift state of mbtowc is not affected.
  If an invalid multibyte character is encountered, the mbstowcs function returns (size_t) - 1. Otherwise, it returns the number of array elements modified, not including a terminating zero code, if any.

size_t wcstombs(char *s, const wchar_t *pwcs, size_t n);

• Converts a sequence of codes that correspond to multibyte characters from the array pointed to by pwcs into a sequence of multibyte characters that begins in the initial shift state, and stores these multibyte characters into the array pointed to by s. The conversion stops if a multibyte character would exceed the limit of n total bytes or if a null character is stored.
  Each code is converted as if by a call to wctomb, except that the shift state of wctomb is not affected.
  If a code is encountered that does not correspond to a valid multibyte character, the wcstombs function returns (size_t) - 1. Otherwise, it returns the number of bytes modified, not including a terminating null character, if any.

The <string.h> header file declares one type and several functions, and defines one macro useful for manipulating character arrays that other objects treat as character arrays.

There are two kinds of string functions declared. The first, with names beginning with str, manipulate character arrays; the second, with names beginning with mem, manipulate other objects treated as character arrays. Except for memmove, function behavior is undefined if copying takes place between overlapping objects.

Type

size_t

• An unsigned integral type of the result of the sizeof operator.

Macro

NULL

• Expands to an implementation-defined null pointer constant.

Functions

void*memcpy(void *s1, const void *s2, size_t n);

• Copies n characters from the object pointed to by s2 to the object pointed to by s1. The function returns s1.

void*memmove(void *s1, const void *s2, size_t n);

• Copies n characters from the object pointed to by s2 to the object pointed to by s1. Copying takes place as if the n characters from the object pointed to by s2 are first copied into a temporary array of n characters that does not overlap the object pointed to by s1 and s2, and then the n characters from the temporary array are copied into the object pointed to by s1. The memmove function returns s1.

void*memchr(const void *s, int c, size_t n);

• Locates the first occurrence of c (converted to an unsigned char) in the first n unsigned characters of the object pointed to by s. The memchr function returns a pointer to the located character, or a null pointer if the character was not found.

int memcmp(const void*s1, const void *s2, size_t n);

• Compares the first n characters of the object pointed to by s1 to the first n characters of the object pointed to by s2. The memcmp function returns an integer less than, equal to, or greater than 0, depending on whether the object pointed to by s1 is less than, equal to, or greater than the object pointed to by s2.

void*memset(void *s, int c, size_t n);

• Copies the value of c (converted to an unsigned char) into each of the first n characters pointed to by s. The function returns s.

char*strcpy(char *s1, const char *s2);

• Copies the string pointed to by s2 (including the terminating null character) to the string pointed to by s1. The strcpy function returns s1.

char*strncpy(char *s1, const char *s2, size_t n);

• Copies no more than n characters from the string pointed to by s2 to the string pointed to by s1, up to but not including the null terminator of the string pointed to by s2; returns s1. If the string pointed to by s2 is less than n characters, strncpy pads the copy with null characters.

char*strcat(char *s1, const char *s2);

• Appends a copy of the the string pointed to by s2 (including the terminating null character) to the end of the string pointed to by s1. The strcat function returns s1. The first character of s2 overwrites the null character of s1.

char*strncat(char *s1, const char *s2, size_t n);

• Appends no more than n characters from the string pointed to by s2 (up to but not including a null character) to the string pointed to by s1. The strncat function returns s1. The first character of s2 overwrites the null character of s1. A terminating null character is appended to the result. The first character of s2 overwrites the null character of s1.

int strcmp(const char*s1, const char *s2);

• Compares the string pointed to by s1 to the string pointed to by s2. The strcmp function returns an integer less than, equal to, or greater than 0, depending on whether the string pointed to by s1 is less than, equal to, or greater than the string pointed to by s2.

int strcoll(const char*s1, const char *s2);

• Compares the string pointed to by s1 to the string pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the current locale (see Section 9.5). The strcoll function returns an integer less than, equal to, or greater than 0, depending on whether the string pointed to by s1 is less than, equal to, or greater than the string pointed to by s2, when both are interpreted as appropriate to the current locale.

int strncmp(const char*s1, const char *s2, size_t n);

• Compares no more than n characters from the string pointed to by s1 to the string pointed to by s2. The strings are compared until a null character is encountered, the strings differ, or n is reached. The strncmp function returns an integer less than, equal to, or greater than 0, depending on whether the string pointed to by s1 is less than, equal to, or greater than the string pointed to by s2.

size_t strxfrm(char *s1, const char *s2, size_t n);

• Transforms the string pointed to by s2 and places the resulting string into the array pointed to by s1.
  See your DEC C library routine documentation for a detailed description of this function.