stdlib.h(0P)

💖 stdlib.h(0P) — POSIX Programmer's Manual 💖

okay bestie, welcome to the manual page for stdlib.h from the POSIX Programmer's Manual — yes that's the standard library definitions, the header that literally everything you've ever written has quietly leaned on. 🫶

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🌸 PROLOG 🌸

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

ngl that's the standard little disclaimer that shows up on all of these, but it's real and it matters — Linux might do its own thing, so if you're on Linux, go check the Linux page too. Don't come for me, I'm just the messenger. 💅

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✨ NAME ✨

stdlib.h — standard library definitions

that's it, that's the name, and honestly it's giving main character of the C standard library. 👑

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🎀 SYNOPSIS 🎀

#include <stdlib.h>

one line, that's the whole vibe. no arguments, no drama. ✨

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💜 DESCRIPTION 💜

okay so here's the tea. Some of the functionality described on this reference page extends the ISO C standard. Which means: applications shall define the appropriate feature test macro (see the System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compilation Environment) to enable the visibility of these symbols in this header. fr fr, no feature test macro, no symbols, no cap. 🚫

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🌈 Macros that expand to integer constant expressions 🌈

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

• EXIT_FAILURE — unsuccessful termination for exit(); it evaluates to a non-zero value. it's giving "we did not slay today" 💀
• EXIT_SUCCESS — successful termination for exit(); it evaluates to 0. the iconic happy ending. ✨
• {RAND_MAX} — maximum value returned by rand(); at least 32767. that's the ceiling, bestie, and it's a lowkey one.

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🦋 The size_t macro 🦋

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

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

and in the POSIX locale, the value of {MB_CUR_MAX} shall be 1. periodt. 💅

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🍓 NULL and friends 🍓

The <stdlib.h> header shall define NULL as described in <stddef.h>.

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🧚 Data types (through typedef) 🧚

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>.

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👑 Wait there's more — symbolic constants and macros 👑

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

all eight of them, we're not skipping a single one, the way that a header just casually hands you wait-status macros. obsessed. 🫶

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💅 The functions 💅

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

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);

look at that list. malloc, free, exit, qsort, strtod, the whole pty crew (grantpt, posix_openpt, ptsname, unlockpt), the entire lrand48 family, and yes, _Exit with the dramatic capital E. it's giving legendary lineup. 🔥

and heads up: inclusion of the <stdlib.h> header may also make visible all symbols from <stddef.h>, <limits.h>, <math.h>, and <sys/wait.h>. surprise bonus content, we love a header that over-shares. 💜

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🙈 Note

The following sections are informative.

so like... read them for context, not for rules. iykyk. 😌

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🌸 APPLICATION USAGE 🌸

None.

literally nothing. the section said "no thoughts, head empty." 💀

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✨ RATIONALE ✨

None.

same energy. nothing here either, bestie. 🎀

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🦋 FUTURE DIRECTIONS 🦋

None.

no plans, no promises, just vibes. ✨

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💖 SEE ALSO 💖

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

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()

that's the whole bestie list, every single one. go read them, they're all iconic in their own right. 👑

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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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and that's the whole page, bestie!! 💅✨ this one came to you courtesy of IEEE/The Open Group, 2017 — stdlib.h(0P), the manual page that ate and left no crumbs. now go #include <stdlib.h> and slay responsibly. 🫶🎀