Standard library header <cstdlib>

 

C++

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Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Standard library headers

Language support
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <stdfloat> (C++23) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11) <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
Concepts
<concepts> (C++20)
Diagnostics
<stdexcept> <stacktrace> (C++23)	<cassert>	<cerrno>	<system_error> (C++11)
Memory management
<memory>	<memory_resource> (C++17)	<scoped_allocator> (C++11)
Metaprogramming
<type_traits> (C++11)	<ratio> (C++11)
General utilities
<utility> <tuple> (C++11) <optional> (C++17) <variant> (C++17)	<any> (C++17) <expected> (C++23) <bitset>	<functional> <typeindex> (C++11) <execution> (C++17)	<charconv> (C++17) <format> (C++20) <bit> (C++20)
Strings
<string_view> (C++17) <string>	<cctype> <cwctype>	<cstring> <cwchar>	<cuchar> (C++11)
Containers
<array> (C++11) <deque> <forward_list> (C++11) <list>	<vector> <map> <set> <unordered_map> (C++11)	<unordered_set> (C++11) <queue> <stack> <flat_map> (C++23)	<flat_set> (C++23) <span> (C++20) <mdspan> (C++23)
Iterators
<iterator>
Ranges
<ranges> (C++20)	<generator> (C++23)
Algorithms
<algorithm>	<numeric>
Numerics
<cfenv> (C++11) <complex>	<random> (C++11) <valarray>	<cmath>	<numbers> (C++20)
Time
<chrono> (C++11)	<ctime>
Localization
<locale>	<clocale>	<codecvt> (C++11/17*)
Input/output
<iosfwd> <iostream> <ios> <streambuf>	<istream> <ostream> <iomanip> <print> (C++23)	<sstream> <spanstream> (C++23) <fstream> <syncstream> (C++20)	<filesystem> (C++17) <cstdio> <cinttypes> (C++11) <strstream> (C++98*)
Regular expressions
<regex> (C++11)
Concurrency support
<stop_token> (C++20) <thread> (C++11) <atomic> (C++11)	<stdatomic.h> (C++23) <mutex> (C++11) <shared_mutex> (C++14)	<condition_variable> (C++11)   <semaphore> (C++20) <latch> (C++20)	<barrier> (C++20) <future> (C++11)
C compatibility
<cstdbool> (C++11/17/20*)   <ccomplex> (C++11/17/20*)	<ctgmath> (C++11/17/20*)	<cstdalign> (C++11/17/20*)	<ciso646> (until C++20)

 

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.

Types
div_t	structure type, returned by std::div (typedef)
ldiv_t	structure type, returned by std::ldiv (typedef)
lldiv_t (C++11)	structure type, returned by std::lldiv (typedef)
size_t	unsigned integer type returned by the sizeof operator (typedef)
Macro constants
EXIT_SUCCESSEXIT_FAILURE	indicates program 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)
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 std::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 or shrinks 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)
atoiatolatoll (C++11)	converts a byte string to an integer value (function)
strtolstrtoll (C++11)	converts a byte string to an integer value (function)
strtoulstrtoull (C++11)	converts a byte string to an unsigned integer value (function)
strtofstrtodstrtold	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)labsllabs (C++11)	computes absolute value of an integral value (\(\small{|x|}\)|x|) (function)
div(int)ldivlldiv (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
  constexpr int abs(int j);
  constexpr long int abs(long int j);
  constexpr long long int abs(long long int j);
  constexpr float abs(float j);
  constexpr double abs(double j);
  constexpr long double abs(long double j);
 
  constexpr long int labs(long int j);
  constexpr long long int llabs(long long int j);
 
  constexpr div_t div(int numer, int denom);
  constexpr ldiv_t div(long int numer, long int denom);
  constexpr lldiv_t div(long long int numer, long long int denom);
  constexpr ldiv_t ldiv(long int numer, long int denom);
  constexpr lldiv_t lldiv(long long int numer, long long int denom);
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 286	C++98	the definition of size_t was not provided in <cstdlib>	provided

See also

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