C Standard Library

Contents

<assert.h>

void assert(int expression);
Macro used to add diagnostics. If expression is false, message printed on stderr and abort called to terminate execution. Source file and line number in message come from preprocessor macros __FILE__ and __LINE__. If NDEBUG is defined where <assert.h> is included, assert macro is ignored.

<ctype.h>

int isalnum(int c);
isalpha(c) or isdigit(c)
int isalpha(int c);
isupper(c) or islower(c)
int iscntrl(int c);
is control character
int isdigit(int c);
is decimal digit
int isgraph(int c);
is printing character other than space
int islower(int c);
is lower-case letter
int isprint(int c);
is printing character (including space)
int ispunct(int c);
is printing character other than space, letter, digit
int isspace(int c);
is space, formfeed, newline, carriage return, tab, vertical tab
int isupper(int c);
is upper-case letter
int isxdigit(int c);
is hexadecimal digit
int tolower(int c);
return lower-case equivalent
int toupper(int c);
return upper-case equivalent
Notes:

<errno.h>

extern int errno;
An error code value set by some functions. It is generally the responsibility of the programmer to clear errno before calling such a function.

<float.h>

FLT_RADIX
FLT_ROUNDS
FLT_DIG
FLT_EPSILON
smallest number x such that 1.0 + x != 1.0
FLT_MANT_DIG
FLT_MAX
maximum floating-point number
FLT_MAX_EXP
FLT_MIN
minimum normalised floating-point number
FLT_MIN_EXP
DBL_DIG
DBL_EPSILON
DBL_MANT_DIG
DBL_MAX
maximum double floating-point number
DBL_MAX_EXP
DBL_MIN
minimum normalised double floating-point number
DBL_MIN_EXP

<limits.h>

CHAR_BIT
number of bits in a char
CHAR_MAX
maximum value of char
CHAR_MIN
minimum value of char
INT_MAX
maximum value of int
INT_MIN
minimum value of int
LONG_MAX
maximum value of long
LONG_MIN
minimum value of long
SCHAR_MAX
maximum value of signed char
SCHAR_MIN
minimum value of signed char
SHRT_MAX
maximum value of short
SHRT_MIN
minimum value of short
UCHAR_MAX
maximum value of unsigned char
UCHAR_MIN
minimum value of unsigned char
UINT_MAX
maximum value of unsigned int
ULONG_MAX
maximum value of unsigned long
USHRT_MAX
maximum value of unsigned short

<math.h>

double sin(double x);
double cos(double x);
double tan(double x);
double asin(double x);
double acos(double x);
double atan(double x);
double atan2(double y, double x);
double sinh(double x);
double cosh(double x);
double tanh(double x);
double exp(double x);
double log(double x);
double log10(double x);
double pow(double x, double y);
x raised to power y
double sqrt(double x);
double ceil(double x);
smallest integer not less than x
double floor(double x);
largest integer not greater than x
double fabs(double x);
double ldexp(double x, int n);
double frexp(double x, int* exp);
double modf(double x, double* ip);
double fmod(double x, double y);

<setjmp.h>

int setjmp(jmp_buf env);
Save state information in env. Zero returned from direct call; non-zero from subsequent call of longjmp.
void longjmp(jmp_buf env, int val);
Restore state saved by most recent call to setjmp using information saved in env. Execution resumes as if setjmp just executed and returned non-zero value val.

<signal.h>

Handling exceptional conditions.
SIGABRT
abnormal termination
SIGFPE
arithmetic error
SIGILL
illegal function image
SIGINT
interactive attention
SIGSEGV
illegal storage access
SIGTERM
termination request sent to program
void (*signal(int sig, void (*handler)(int)))(int);
Install handler for subsequent signal sig. If handler is SIG_DFL, implementation-defined default behaviour is used; if handler is SIG_IGN, signal is ignored; otherwise function pointed to by handler is called with argument sig. signal returns the previous handler or SIG_ERR on error. When signal sig subsequently occurs, the signal is restored to its default behaviour and the handler is called. If the handler returns, execution resumes where signal occurred. Initial state of signals is implementation-defined.
int raise(int sig);
Send signal sig to the program. Non-zero returned if unsuccessful.

<stdarg.h>

Facilities for stepping through a list of function arguments of unknown number and type.
void va_start(va_list ap, lastarg);
Initialisation macro to be called once before any unnamed argument is accessed. ap must be declared as a local variable, and lastarg is the last named parameter of the function.
type va_arg(va_list ap, type);
Produce a value of the type (type) and value of the next unnamed argument. Modifies ap.
void va_end(va_list ap);
Must be called once after arguments processed and before function exit.

<stdio.h>

FILE
Type which records information necessary to control a stream.
stdin
Standard input stream. Automatically opened when a program begins execution.
stdout
Standard output stream. Automatically opened when a program begins execution.
stderr
Standard error stream. Automatically opened when a program begins execution.
FILENAME_MAX
Maximum permissible length of a file name
FOPEN_MAX
Maximum number of files which may be open simultaneously.
TMP_MAX
Maximum number of temporary files during program execution.
FILE* fopen(const char* filename, const char* mode);
Opens file filename and returns a stream, or NULL on failure. mode may be (combinations of):
"r"
text reading
"w"
text writing; discard previous content
"a"
text append; writing at end
"r+"
text update
"w+"
text update; discard previous content
"a+"
text append; writing at end
FILE* freopen(const char* filename, const char* mode, FILE* stream);
Opens file filename with the specified mode and associates with it the specified stream. Returns stream or NULL on error. Usually used to change files associated with stdin, stdout, stderr.
int fflush(FILE* stream);
Flushes stream stream. Effect undefined for input stream. Returns EOF for write error, zero otherwise. fflush(NULL) flushes all output streams.
int fclose(FILE* stream);
Closes stream stream (after flushing, if output stream). Returns EOF on error, zero otherwise.
int remove(const char* filename);
Removes file filename. Returns non-zero on failure.
int rename(const char* oldname, const char* newname);
Changes name of file oldname to newname. Returns non-zero on failure.
FILE* tmpfile();
Creates temporary file (mode "wb+") which will be removed when closed or on normal program termination. Returns stream or NULL on failure.
char* tmpname(char s[L_tmpnam]);
Assigns to s and returns unique name for temporary file.
int setvbuf(FILE* stream, char* buf, int mode, size_t size);
Controls buffering for stream stream.
void setbuf(FILE* stream, char* buf);
Controls buffering for stream stream.
int fprintf(FILE* stream, const char* format, ...);
Converts (with format format) and writes output to stream stream. Number of characters written [negative on error] is returned. Between % and format conversion character: Conversions:
d, i
int; signed decimal notation
o
int; unsigned octal notation
x,X
int; unsigned hexadecimal notation
u
int; unsigned decimal notation
c
int; single character
s
char*;
f
double; [-]mmm.ddd
e,E
double; [-]m.dddddde(+|-)xx
g,G
double
p
void*; print as pointer
n
int*; number of chars written into arg
%
print %
int printf(const char* format, ...);
printf(f, ...) is equivalent to fprintf(stdout, f, ...)
int sprintf(char* s, const char* format, ...);
Like fprintf, but output written into string s, which must be large enough to hold the output, rather than to a stream. Output is NUL-terminated. Return length does not include the NUL.
int vfprintf(FILE* stream, const char* format, va_list arg);
Equivalent to fprintf except that the variable argument list is replaced by arg, which must have been initialised by the va_start macro and may have been used in calls to va_arg. See <stdarg.h>
int vprintf(const char* format, va_list arg);
Equivalent to printf except that the variable argument list is replaced by arg, which must have been initialised by the va_start macro and may have been used in calls to va_arg. See <stdarg.h>
int vsprintf(char* s, const char* format, va_list arg);
Equivalent to sprintf except that the variable argument list is replaced by arg, which must have been initialised by the va_start macro and may have been used in calls to va_arg. See <stdarg.h>
int fscanf(FILE* stream, const char* format, ...);
Performs formatted input conversion, reading from stream stream according to format format. The function returns when format is fully processed. Returns EOF if end-of-file or error occurs before any conversion; otherwise, the number of items converted and assigned. Each of the arguments following format must be a pointer. Format string may contain Conversion characters:
d
decimal integer; int* parameter required
i
integer; int* parameter required; decimal, octal or hex
o
octal integer; int* parameter required
u
unsigned decimal integer; unsigned int* parameter required
x
hexadecimal integer; int* parameter required
c
characters; char* parameter required; up to width; no '\0' added; no skip
s
string of non-white-space; char* parameter required; '\0' added
e,f,g
floating-point number; float* parameter required
p
pointer value; void* parameter required
n
chars read so far; int* parameter required
[...]
longest non-empty string from set; char* parameter required; '\0'
[^...]
longest non-empty string not from set; char* parameter required; '\0'
%
literal %; no assignment
int scanf(const char* format, ...);
scanf(f, ...) is equivalent to fscanf(stdin, f, ...)
int sscanf(char* s, const char* format, ...);
Like fscanf, but input read from string s.
int fgetc(FILE* stream);
Returns next character from stream stream as an unsigned char, or EOF on end-of-file or error.
char* fgets(char* s, int n, FILE* stream);
Reads at most the next n-1 characters from stream stream into s, stopping if a newline is encountered (after copying the newline to s). s is NUL-terminated. Returs s, or EOF on end-of-file or error.
int fputc(int c, FILE* stream);
Writes c, converted to unsigned char, to stream stream. Returns the character written, or EOF on error.
char* fputs(const char* s, FILE* stream);
Writes s, which need not contain '\n' on stream stream. Returns non-negative on success, EOF on error.
int getc(FILE* stream);
Equivalent to fgetc except that it may be a macro.
int getchar();
Equivalent to getc(stdin).
char* gets(char* s);
Reads next line from stdin into s. Replaces terminating newline with '\0'. Returns s, or NULL on end-of-file or error.
int putc(int c, FILE* stream);
Equivalent to fputc except that it may be a macro.
int putchar(int c);
putchar(c) is equivalent to putc(c, stdout).
int puts(const char* s);
Writes s and a newline to stdout. Returns non-negative on success, EOF on error.
int unget(int c, FILE* stream);
Pushes c (which must not be EOF), converted to unsigned char, onto stream stream such that it will be returned by the next read. Only one character of pushback is guaranteed for a stream. Returns c, or EOF on error.
size_t fread(void* ptr, size_t size, size_t nobj, FILE* stream);
Reads at most nobj objects of size size from stream stream into ptr. Returns the number of objects read. feof and ferror must be used to determine status.
size_t fwrite(const void* ptr, size_t size, size_t nobj, FILE* stream);
Writes to stream stream, nobj objects of size size from array ptr. Returns the number of objects written (which will be less than nobj on error).
int fseek(FILE* stream, long offset, int origin);
Sets file position for stream stream. For a binary file, position is set to offset characters from origin, which may be SEEK_SET (beginning), SEEK_CUR(current position) or SEEK_END (end-of-file); for a text stream, offset must be zero or a value returned by ftell (in which case origin must be SEEK_SET). Returns non-zero on error.
long ftell(FILE* stream);
Returns current file position for stream stream, or -1L on error.
void rewind(FILE* stream);
rewind(stream) is equivalent to fseek(stream, 0L, SEEK_SET); clearerr(stream).
int fgetpos(FILE* stream, fpos_t* ptr);
Assigns current position in stream stream to *ptr. Type fpos_t is suitable for recording such values. Returns non-zero on error.
int fsetpos(FILE* stream, const fpos_t* ptr);
Sets current position of stream stream to *ptr. Returns non-zero on error.
void clearerr(FILE* stream);
Clears the end-of-file and error indicators for stream stream.
int feof(FILE* stream);
Returns non-zero if end-of-file indicator for stream stream is set.
int ferror(FILE* stream);
Returns non-zero if error indicator for stream stream is set.
void perror(const char* s);
Prints s and implementation-defined error message corresponding to errno:
fprintf(stderr, "%s: %s\n", s, "error message")
See strerror.

<stdlib.h>

double atof(const char* s);
Returns numerical value of s. Equivalent to strtod(s, (char**)NULL).
int atoi(const char* s);
Returns numerical value of s. Equivalent to (int)strtol(s, (char**)NULL, 10).
long atol(const char* s);
Returns numerical value of s. Equivalent to strtol(s, (char**)NULL, 10).
double strtod(const char* s, char** endp);
Converts prefix of s to double, ignoring leading quite space. Stores a pointer to any unconverted suffix in *endp if endp non-NULL. If answer would overflow, HUGE_VAL is returned with the appropriate sign; if underflow, zero returned. In either case, errno is set to ERANGE.
long strtol(const char* s, char** endp, int base);
Converts prefix of s to long, ignoring leading quite space. Stores a pointer to any unconverted suffix in *endp if endp non-NULL. If base between 2 and 36, that base used; if zero, leading 0X or 0x implies hexadecimal, leading 0implies octal, otherwise decimal. Leading 0X or 0x permitted for base 16. If answer would overflow, LONG_MAX or LONG_MIN returned and errno is set to ERANGE.
unsigned long strtoul(const char* s, char** endp, int base);
As for strtol except result is unsigned long and error value is ULONG_MAX.
int rand();
Returns pseudo-random number in range 0 to RAND_MAX.
void srand(unsigned int seed);
Uses seed as seed for new sequence of pseudo-random numbers. Initial seed is 1.
void* calloc(size_t nobj, size_t size);
Returns pointer to zero-initialised newly-allocated space for an array of nobj objects each of size size, or NULL if request cannot be satisfied.
void* malloc(size_t size);
Returns pointer to uninitialised newly-allocated space for an object of size size, or NULL if request cannot be satisfied.
void* realloc(void* p, size_t size);
Changes to size the size of the object to which p points. Contents unchanged to minimum of old and new sizes. If new size larger, new space is uninitialised. Returns ponter to the new space or, if request cannot be satisfied NULL leaving p unchanged.
void free(void* p);
Deallocats space to which p points. p must be NULL, in which case there is no effect, or a pointer returned by calloc, malloc or realloc.
void abort();
Causes program to terminate abnormally, as if by raise(SIGABRT).
void exit(int status);
Causes normal program termination. Functions installed using atexit are called in reverse order of registration, open files are flushed, open streams are closed and control is returned to environment. status is returned to environment in implementation-dependent manner. Zero indicates successful termination and the values EXIT_SUCCESS and EXIT_FAILURE may be used.
int atexit(void (*fcm)(void));
Registers fcn to be called when program terminates normally. Non-zero returned if registration cannot be made.
int system(const char* s);
Passes s to environment for execution. If s is NULL, non-zero returned if command processor exists; return value is implementation-dependent if s is non-NULL.
char getenv(const char* name);
Returns (implementation-dependent) environment string associated with name, or NULL if no such string exists.
void bsearch(const void* key, const void* base, size_t n, size_t size, int (*cmp)(const void* keyval, const void* datum);
Searches base[0]...base[n-1] for item matching *key. Comparison function cmp must return negative if first argument is less than second, zero if equal and positive if greater. The n items of base must be in ascending order. Returns a pointer to the matching entry or NULL if not found.
void qsort(void* base, size_t n, size_t size, int (*cmp)(const void*, const void/);
Arranges into ascending order the array base[0]...base[n-1] of objects of size size. Comparison function cmp must return negative if first argument is less than second, zero if equal and positive if greater.
int abs(int n);
Returns absolute value of n
long labs(long n);
Returns absolute value of n
div_t div(int num, int denom);
Returns in fields quot and rem of structure of type div_t the quotient and remainder of num/denom.
ldiv_t ldiv(long num, long denom);
Returns in fields quot and rem of structure of type ldiv_t the quotient and remainder of num/denom.

<string.h>

char* strcpy(char* s, const char* ct);
Copy ct to s including terminating NUL. Return s.
char* strncpy(char* s, const char* ct, int n);
Copy at most n characters of ct to s Pad with NULs if ct is of length less than n. Return s.
char* strcat(char* s, const char* ct);
Concatenate ct to s. Return s.
char* strncat(char* s, const char* ct, int n);
Concatenate at most n characters of ct to s. Terminate s with NUL and return it.
int strcmp(const char* cs, const char* ct);
Compare cs and ct. Return negative if cs < ct, zero if cs == ct, positive if cs > ct.
int strncmp(const char* cs, const char* ct, int n);
Compare at most n characters of cs and ct. Return negative if cs < ct, zero if cs == ct, positive if cs > ct.
char* strchr(const char* cs, int c);
Return pointer to first occurrence of c in cs, or NULL if not found.
char* strrchr(const char* cs, int c);
Return pointer to last occurrence of c in cs, or NULL if not found.
size_t strspn(const char* cs, const char* ct);
Return length of prefix of cs consisting entirely of characters in ct.
size_t strcspn(const char* cs, const char* ct);
Return length of prefix of cs consisting entirely of characters not in ct.
char* strpbrk(const char* cs, const char* ct);
Return pointer to first occurrence within cs of any character of ct, or NULL if not found.
char* strstr(const char* cs, const char* ct);
Return pointer to first occurrence of ct in cs, or NULL if not found.
size_t strlen(const char* cs);
Return length of cs.
char* strerror(int n);
Return pointer to implementation-defined string corresponding with error n.
char* strtok(char* s, const char* t);
A sequence of calls to strtok returns tokens from s delimted by a character in ct. Non-NULL s indicates the first call in a sequence. ct may differ on each call. Returns NULL when no such token found.
void* memcpy(void* s, const void* ct, int n);
Copy n characters from ct to s. Return s. Does not work correctly if objects overlap.
void* memmove(void* s, const void* ct, int n);
Copy n characters from ct to s. Return s. Works correctly even if objects overlap.
int memcmp(const void* cs, const void* ct, int n);
Compare first n characters of cs with ct. Return negative if cs < ct, zero if cs == ct, positive if cs > ct.
void* strchr(const char* cs, int c, int n);
Return pointer to first occurrence of c in first n characters of cs, or NULL if not found.
void* strchr(char* s, int c, int n);
Replace each of the first n characters of s by c. Return s.

<time.h>

clock_t
An arithmetic type representing time.
CLOCKS_PER_SEC
The number of clock_t units per second.
time_t
An arithmetic type representing time.
struct tm
Represents the components of calendar time:
int tm_sec;
seconds after the minute
int tm_min;
minutes after the hour
int tm_hour;
hours since midnight
int tm_mday;
day of the month
int tm_ymon;
months since January
int tm_year;
years since 1900
int tm_day;
days since Sunday
int tm_yday;
days since January 1
int tm_isdst;
Daylight Saving Time flag : is positive if DST is in effect, zero if not in effect, negative if information unavailable.
clock_t clock();
Returns processor time used by program or -1 if not available.
time_t time(time_t* tp);
Returns current calendar time or -1 if not available. If tp is non-NULL, return value is also assigned to *tp.
double difftime(time_t time2, time_t time1);
Returns the difference is seconds between time2 and time1.
time_t mktime(struct tm* tp);
Returns the local time corresponding to *tp, or -1 if it cannot be represented.
char* asctime(const struct tm* tp);
Returns the given time as a string of the form:
Sun Jan 3 14:14:13 1988\n\0
char* ctime(const time_t tp);
Converts the given calendar time to a local time and returns the equivalent string. Equivalent to:
asctime(localtime(tp))
struct tm* gmtime(const time_t tp);
Returns the given calendar time converted into Coordinated Universal Time, or NULL if not available.
struct tm* localtime(const time_t tp);
Returns calendar time *tp converted into local time.
size_t strftime(char* s, size_t smax, const char* fmt, const struct tm* tp);
Formats *tp into s according to fmt.
Notes: