stdlib.h(7POSIX)

✨ PROLOG ✨

okay bestie, before we even get into it, real talk: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so go check the corresponding Linux manual page for the tea ☕), or honestly the interface might not even be implemented on Linux at all. Not every platform is on the same vibe. 💅

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🎀 NAME 🎀

stdlib.h — standard library definitions

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🦋 SYNOPSIS 🦋

#include <stdlib.h>

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🌸 DESCRIPTION 🌸

okay so some of the functionality on this page actually extends the ISO C standard. If you want those extra symbols to show up, your application has to define the appropriate feature test macro (peep the System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compilation Environment). No macro, no visibility. That's just how it is. 😭

The <stdlib.h> header shall define the following macros, and they shall expand to integer constant expressions:

• EXIT_FAILURE — unsuccessful termination for exit(); evaluates to a non-zero value. 💀
• EXIT_SUCCESS — successful termination for exit(); evaluates to 0. we love a clean exit. 🫶
• {RAND_MAX} — the maximum value returned by rand(); at least 32767.

The <stdlib.h> header shall also define the following macro, which shall expand to a positive integer expression with type size_t:

• {MB_CUR_MAX} — the maximum number of bytes in a character specified by the current locale (category LC_CTYPE).

And heads up: in the POSIX locale, the value of {MB_CUR_MAX} shall be 1. periodt.

The <stdlib.h> header shall define NULL as described in <stddef.h>. (yes, that's where it lives, iykyk)

The <stdlib.h> header shall define the following data types through typedef:

• div_t — structure type returned by the div() function.
• ldiv_t — structure type returned by the ldiv() function.
• lldiv_t — structure type returned by the lldiv() function.
• size_t — as described in <stddef.h>.
• wchar_t — as described in <stddef.h>.

In addition, the <stdlib.h> header shall define the following symbolic constants and macros as described in <sys/wait.h>:

• WEXITSTATUS
• WIFEXITED
• WIFSIGNALED
• WIFSTOPPED
• WNOHANG
• WSTOPSIG
• WTERMSIG
• WUNTRACED

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided. (this list is long bestie, hydrate before reading 💧)

void          _Exit(int);
long          a64l(const char *);
void          abort(void);
int           abs(int);
int           atexit(void (*)(void));
double        atof(const char *);
int           atoi(const char *);
long          atol(const char *);
long long     atoll(const char *);
void         *bsearch(const void *, const void *, size_t, size_t,
                  int (*)(const void *, const void *));
void         *calloc(size_t, size_t);
div_t         div(int, int);
double        drand48(void);
double        erand48(unsigned short [3]);
void          exit(int);
void          free(void *);
char         *getenv(const char *);
int           getsubopt(char **, char *const *, char **);
int           grantpt(int);
char         *initstate(unsigned, char *, size_t);
long          jrand48(unsigned short [3]);
char         *l64a(long);
long          labs(long);
void          lcong48(unsigned short [7]);
ldiv_t        ldiv(long, long);
long long     llabs(long long);
lldiv_t       lldiv(long long, long long);
long          lrand48(void);
void         *malloc(size_t);
int           mblen(const char *, size_t);
size_t        mbstowcs(wchar_t *restrict, const char *restrict, size_t);
int           mbtowc(wchar_t *restrict, const char *restrict, size_t);
char         *mkdtemp(char *);
int           mkstemp(char *);
long          mrand48(void);
long          nrand48(unsigned short [3]);
int           posix_memalign(void **, size_t, size_t);
int           posix_openpt(int);
char         *ptsname(int);
int           putenv(char *);
void          qsort(void *, size_t, size_t, int (*)(const void *,
                  const void *));
int           rand(void);
int           rand_r(unsigned *);
long          random(void);
void         *realloc(void *, size_t);
char         *realpath(const char *restrict, char *restrict);
unsigned short *seed48(unsigned short [3]);
int           setenv(const char *, const char *, int);
void          setkey(const char *);
char         *setstate(char *);
void          srand(unsigned);
void          srand48(long);
void          srandom(unsigned);
double        strtod(const char *restrict, char **restrict);
float         strtof(const char *restrict, char **restrict);
long          strtol(const char *restrict, char **restrict, int);
long double   strtold(const char *restrict, char **restrict);
long long     strtoll(const char *restrict, char **restrict, int);
unsigned long strtoul(const char *restrict, char **restrict, int);
unsigned long long
              strtoull(const char *restrict, char **restrict, int);
int           system(const char *);
int           unlockpt(int);
int           unsetenv(const char *);
size_t        wcstombs(char *restrict, const wchar_t *restrict, size_t);
int           wctomb(char *, wchar_t);

Sneaky bonus: including the <stdlib.h> header may also make visible all symbols from <stddef.h>, <limits.h>, <math.h>, and <sys/wait.h>. surprise! 🎁

the following sections are informative. which is fancy-speak for "not the binding rules, just context."

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🙈 APPLICATION USAGE 🙈

None. literally nothing. it's giving minimalism. ✨

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💜 RATIONALE 💜

None. again, nothing. iconic behavior honestly.

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🌈 FUTURE DIRECTIONS 🌈

None. the future is... also nothing. 🔮

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👑 SEE ALSO 👑

• <limits.h>
• <math.h>
• <stddef.h>
• <sys_types.h>
• <sys_wait.h>

And from the System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compilation Environment: _Exit(), a64l(), abort(), abs(), atexit(), atof(), atoi(), atol(), bsearch(), calloc(), div(), drand48(), exit(), free(), getenv(), getsubopt(), grantpt(), initstate(), labs(), ldiv(), malloc(), mblen(), mbstowcs(), mbtowc(), mkdtemp(), posix_memalign(), posix_openpt(), ptsname(), putenv(), qsort(), rand(), realloc(), realpath(), setenv(), setkey(), strtod(), strtol(), strtoul(), system(), unlockpt(), unsetenv(), wcstombs(), wctomb()

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💖 COPYRIGHT 💖

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay that's the whole page bestie, you ate that 💅✨

and for the cute sign-off: this whole thing is brought to you by IEEE/The Open Group, dated 2017 — that's the <pink>stdlib.h(7POSIX)</pink> energy, no cap. 🎀🦋