C stdlib.h Reference

C stdlib.h

atof(): Converts a string to a double-precision floating-point number, stopping at the first non-numeric character.
atoi(): Converts a string to an integer, stopping at the first non-numeric character. Deprecated in favor of strtol() for better error handling.
atol(): Converts a string to a long integer, stopping at the first non-numeric character.
atoll(): Converts a string to a long long integer, stopping at the first non-numeric character.
strtod(): Converts a string to a double-precision floating-point number, providing better error handling than atof().
strtof(): Converts a string to a single-precision floating-point number (float), stopping at the first invalid character.
strtol(): Converts a string to a long integer with support for different numerical bases and error handling.
strtold(): Converts a string to a long double floating-point number, providing higher precision than strtod().
strtoll(): Converts a string to a long long integer, supporting different numerical bases and error handling.
strtoul(): Converts a string to an unsigned long integer, supporting different numerical bases and error handling.
strtoull(): Converts a string to an unsigned long long integer, supporting different numerical bases and error handling.

rand(): Generates a pseudo-random integer in the range 0 to RAND_MAX, using a linear congruential generator.
srand(): Seeds the random number generator with a specified value, allowing rand() to produce different sequences of random numbers.

calloc(): Allocates memory for an array of elements, initializes all bytes to zero, and returns a pointer to the allocated memory.
free(): Deallocates a previously allocated memory block, freeing up system memory.
malloc(): Allocates a specified number of bytes in memory and returns a pointer to the allocated block. The memory is uninitialized.
realloc(): Resizes a previously allocated memory block while preserving its contents if possible. If a new block is allocated, the old data is copied.

abort(): Immediately terminates the calling process abnormally, without executing cleanup functions or flushing streams.
atexit(): Registers a function to be executed when exit() is called, useful for cleanup operations.
at_quick_exit(): Registers a function to be executed when quick_exit() is called, similar to atexit() but used for faster termination.
exit(): Terminates the calling process normally, performing cleanup functions such as closing open file streams.
getenv(): Retrieves the value of an environment variable as a string, allowing access to system configuration data.
quick_exit(): Terminates the calling process quickly, executing functions registered with at_quick_exit() but skipping some cleanup operations.
system(): Executes a system command by passing a string to the host environment’s command processor.
_Exit(): Terminates the calling process immediately, skipping cleanup functions and flushing of output streams.

bsearch(): Performs a binary search on a sorted array, returning a pointer to the matching element if found, or NULL if not found.
qsort(): Sorts an array using the quicksort algorithm, requiring a user-defined comparison function to determine element order.

abs(): Returns the absolute value of an integer, ensuring the result is always non-negative.
div(): Performs integer division and returns a structure containing both the quotient and remainder.
labs(): Returns the absolute value of a long integer.
ldiv(): Performs division on long integers and returns a structure containing both the quotient and remainder.
llabs(): Returns the absolute value of a long long integer.
lldiv(): Performs division on long long integers and returns a structure containing both the quotient and remainder.

mblen(): Determines the number of bytes in a multibyte character, given the current locale.
mbtowc(): Converts a multibyte character sequence into a wide character, based on the current locale.
wctomb(): Converts a wide character into its corresponding multibyte sequence.

mbstowcs(): Converts a multibyte character string into a wide-character string, based on the current locale.
wcstombs(): Converts a wide-character string into a multibyte character string, based on the current locale.