# Standard library header <cstdlib>

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This header was originally in the C standard library as `<stdlib.h>`.

This header provides miscellaneous utilities. Symbols defined here are used by several library components.

### Macro constants

EXIT_SUCCESS EXIT_FAILURE | indicates program execution execution status (macro constant)
MB_CUR_MAX | maximum number of bytes in a multibyte character with the current locale (macro constant)
NULL | implementation-defined null pointer constant (macro constant)
RAND_MAX | maximum possible value generated by std::rand (macro constant)

### Types

div_t | structure type, return of the std::div function (typedef)
ldiv_t | structure type, return of the std::ldiv function (typedef)
lldiv_t (C++11) | structure type, return of the std::lldiv function (typedef)
size_t | unsigned integer type returned by the `sizeof` operator (typedef)

### Functions

##### Process control

abort | causes abnormal program termination (without cleaning up) (function)
exit | causes normal program termination with cleaning up (function)
quick_exit (C++11) | causes quick program termination without completely cleaning up (function)
_Exit (C++11) | causes normal program termination without cleaning up (function)
atexit | registers a function to be called on std::exit() invocation (function)
at_quick_exit (C++11) | registers a function to be called on `quick_exit` invocation (function)
system | calls the host environment's command processor (function)
getenv | access to the list of environment variables (function)

##### Memory management

malloc | allocates memory (function)
aligned_alloc (C++17) | allocates aligned memory (function)
calloc | allocates and zeroes memory (function)
realloc | expands previously allocated memory block (function)
free | deallocates previously allocated memory (function)

##### Numeric string conversion

atof | converts a byte string to a floating point value (function)
atoi atol atoll | converts a byte string to an integer value (function)
strtol strtoll | converts a byte string to an integer value (function)
strtoul strtoull | converts a byte string to an unsigned integer value (function)
strtof strtod strtold | converts a byte string to a floating point value (function)

##### Wide string manipulation

mblen | returns the number of bytes in the next multibyte character (function)
mbtowc | converts the next multibyte character to wide character (function)
wctomb | converts a wide character to its multibyte representation (function)
mbstowcs | converts a narrow multibyte character string to wide string (function)
wcstombs | converts a wide string to narrow multibyte character string (function)

##### Miscellaneous algorithms and math

rand | generates a pseudo-random number (function)
srand | seeds pseudo-random number generator (function)
qsort | sorts a range of elements with unspecified type (function)
bsearch | searches an array for an element of unspecified type (function)
abs(int)labs llabs (C++11) | computes absolute value of an integral value (|x|) (function)
div(int)ldiv lldiv (C++11) | computes quotient and remainder of integer division (function)

### Synopsis

    namespace std {
      using size_t = /*see description*/ ;
      using div_t = /*see description*/ ;
      using ldiv_t = /*see description*/ ;
      using lldiv_t = /*see description*/ ;
    }
    #define NULL /*see description*/
    #define EXIT_FAILURE /*see description*/
    #define EXIT_SUCCESS /*see description*/
    #define RAND_MAX /*see description*/
    #define MB_CUR_MAX /*see description*/
    namespace std {
      // Exposition-only function type aliases
      extern "C" using /*c-atexit-handler*/ = void(); // exposition only
      extern "C++" using /*atexit-handler*/ = void(); // exposition only
      extern "C" using /*c-compare-pred*/ = int(const void* , const void*); // exposition only
      extern "C++" using /*compare-pred*/ = int(const void* , const void*); // exposition only
      // start and termination
      [[noreturn]] void abort() noexcept;
      int atexit(/*c-atexit-handler*/ * func) noexcept;
      int atexit(/*atexit-handler*/ * func) noexcept;
      int at_quick_exit(/*c-atexit-handler*/ * func) noexcept;
      int at_quick_exit(/*atexit-handler*/ * func) noexcept;
      [[noreturn]] void exit(int status);
      [[noreturn]] void _Exit(int status) noexcept;
      [[noreturn]] void quick_exit(int status) noexcept;
      char* getenv(const char* name);
      int system(const char* string);
      // C library memory allocation
      void* aligned_alloc(size_t alignment, size_t size);
      void* calloc(size_t nmemb, size_t size);
      void free(void* ptr);
      void* malloc(size_t size);
      void* realloc(void* ptr, size_t size);
      double atof(const char* nptr);
      int atoi(const char* nptr);
      long int atol(const char* nptr);
      long long int atoll(const char* nptr);
      double strtod(const char* nptr, char** endptr);
      float strtof(const char* nptr, char** endptr);
      long double strtold(const char* nptr, char** endptr);
      long int strtol(const char* nptr, char** endptr, int base);
      long long int strtoll(const char* nptr, char** endptr, int base);
      unsigned long int strtoul(const char* nptr, char** endptr, int base);
      unsigned long long int strtoull(const char* nptr, char** endptr, int base);
      // multibyte / wide string and character conversion functions
      int mblen(const char* s, size_t n);
      int mbtowc(wchar_t* pwc, const char* s, size_t n);
      int wctomb(char* s, wchar_t wchar);
      size_t mbstowcs(wchar_t* pwcs, const char* s, size_t n);
      size_t wcstombs(char* s, const wchar_t* pwcs, size_t n);
      // C standard library algorithms
      void* bsearch(const void* key, const void* base,
                    size_t nmemb, size_t size, /*c-compare-pred*/ * compar);
      void* bsearch(const void* key, const void* base,
                    size_t nmemb, size_t size, /*compare-pred*/ * compar);
      void qsort(void* base, size_t nmemb, size_t size, /*c-compare-pred*/ * compar);
      void qsort(void* base, size_t nmemb, size_t size, /*compare-pred*/ * compar);
      // low-quality random number generation
      int rand();
      void srand(unsigned int seed);
      // absolute values
      int abs(int j);
      long int abs(long int j);
      long long int abs(long long int j);
      float abs(float j);
      double abs(double j);
      long double abs(long double j);
      long int labs(long int j);
      long long int llabs(long long int j);
      div_t div(int numer, int denom);
      ldiv_t div(long int numer, long int denom);
      lldiv_t div(long long int numer, long long int denom);
      ldiv_t ldiv(long int numer, long int denom);
      lldiv_t lldiv(long long int numer, long long int denom);
    }

### See Also

- Program support utilities
- Pseudo-random number generation
- Common mathematical functions
- C memory management library
- Null-terminated byte strings
- Null-terminated multibyte strings
- Algorithms library

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