C Standard Library - C Programming

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C Standard Library Reference

Syntax Description

#include <stdio.h> standard input and output functions

#include <stdlib.h> conversions & allocations functions

#include <ctype.h> characters testing functions

#include <string.h> string manipulation functions

#include <math.h> mathematical functions

#include <time.h> date & time functions

#include <limits.h> data types range constants

#include <float.h> floating point data types range constants

stdio.h

Syntax Description

FILE *fopen(const char *name,
             const char *mode)
file open

FILE *freopen(const char *name,
               const char *mode,
               FILE *fp)
file reopen

int    fclose(FILE *fp) file close

size_t fread(void  *ptr,
             size_t size,

             size_t n,

             FILE *fp)
file read

size_t fwrite(const void *ptr,
              size_t size,

              size_t n,

              FILE *fp)
file write

int   feof(FILE *fp) check file pointer for end of file

int    fseek(FILE *fp,
           long offset,

             int mode)
set file position

int    fflush(FILE *fp) file flush

long ftell(FILE *fp) get file position

void rewind(FILE *fp) set file position to start of file

int    fgetpos(FILE *fp,
             fpos_t *ptr)
write file position in *ptr

int    fsetpos(FILE *fp,
               const fpos_t *ptr)
set file position from *ptr

int    rename(const char *oldname,
           const char *newname)
rename file

int    remove(const char *name) delete file

FILE *tmpfile(void) creates temporary binary file - will be deleted after program ends

char *tmpnam(char *str) get temporary (not opened) filename string

void setbuf(FILE *fp, char *buf) set stream buffering

int   setvbuf(FILE *fp,
               char *buf,

               int mode, size_t size)
set stream buffering

int    printf(const char *format,
              ...)
formatted output to stdout

int    sprintf(const char *str,
               const char *format,

               ...)
formatted output to string

int    fprintf(FILE *fp,
               const char *format,

               ...)
formatted output to file

int    scanf(const char *format, ...) formatted input from stdin

int    fscanf(FILE *fp,
              const char *format, ...)
formatted input from file

int    sscanf(const char *str,
              const char *format, ...)
formatted input from string

int    getchar(void) read character from stdin

int    getc(FILE *fp) read character from file stream

int    fgetc(FILE *fp) read character from file stream

int    putchar(int c) write character to stdout

int    putc(int c, FILE *fp) write character from file stream

int    fputc(int c, FILE *fp) write character from file stream

int    ungetc(int c, FILE *fp)

char *gets(char *str) read line from stdin

char *fgets(char *str, int n,
            FILE *fp)
read line from file stream

int    puts(const char *str) write line to stdout

int    fputs(const char *str,
             FILE *fp)
write line to file stream

void clearerr(FILE *fp) clear file eof and error flags

int   ferror(FILE *fp) check file pointer for file error

void perror(const char *str) print error message to stderr

stdlib.h

Syntax Description

void *malloc(size_t size) allocate memory

void *realloc(void *ptr, size_t size) reallocate memory

void *calloc(size_t objnum,
              size_t objnum)
allocate memory of objnum*objnum

void   free(void *ptr) free allocated memory

double atof(const char *str) numeral string conversion to double

int    atoi(const char *str) numeral string conversion to integer

long atol(const char *str) numeral string conversion to long

double strtod(const char *str,
              char **endptr)
numeral string conversion to double

long   strtol(const char *str,
              char **endptr, int base)
numeral string conversion to long

unsigned long
       strtoul(const char *str,

               char **endptr,
               int base)
numeral string conversion to unsigned long

void   exit(int status) normal program termination

void   abort(void) abnormal program termination

char *getenv(const char *name) get environment variable

int    atexit(void (*funcptr)(void)) register function call at program exit

int    system(const char *command) executes system shell command

int    rand(void) random integer in 0..RAND_MAX

void   srand(unsigned int seed) set random sequence seed

int    abs(int x) absolute value: |x|

long   labs(long x) absolute value: |x|

div_t div(int x, int y) calculates quotient and reminder of x/y

ldiv_t ldiv(long x, long y) calculates quotient and reminder of x/y

void   bsearch(const void *key,
         const void *base,

         size_t nobj,

         size_t size,

         int (*comp)

         (const void *,const void *))
binary search of a sorted array

void   qsort(void *base, size_t nobj,
         size_t size,

         int (*comp)

         (const void *,const void *))
quick sort

string.h

Syntax Description

void *memcpy(void *psrc,
              const void *pdest,

              size_t n)
memory copy of n bytes from psrc to pdest

int    memcmp(const void *p1,
              const void *p2,

              size_t n)
memory compare of n bytes in p1 and p2

void *memmove(void *p1,
               const void *p2,

               size_t n)
memory copy of n bytes from p2 to p1

void *memset(const void *p,
              int c, size_t n)
memory character set of c in p..p+n-1 addresss range

void *memchr(const void *p,
              int c, size_t n)
memory character search for c in p..p+n-1 addresss range

size_t strlen(const char *str) string length (without '\0')

char *strcpy(char *dest,
              const char *src)
copy string src to dest

char *strncpy(char *dest,
               const char *src,

               size_t n)
copy up to n characters from src to dest

char *strcat(char *str1,
              const char *str2)
concatenate str1 and str2 and store in str1

char *strncat(char *str1,
               const char *str2,

               size_t n)
concatenate str1 and up to n characters from str2 and store in str1

int    strcmp(const char *str1,
              const char *str2)
compare str1 and str2 strings

int    strncmp(const char *str1,
               const char *str2,

               size_t n)
compares up to n characters of str1 and str2 strings

char *strchr(const char *str,
              int c)
look for first char c in str

char *strrchr(const char *str,
               int c)
look for last char c in str

size_t strspn(const char *str1,
              const char *str2)
find the intersection string of str1 and str2

size_t strcspn(const char *str1,
               const char *str2)
find the not intersection string of str1 and str2

char *strpbrk(const char *str,
               const char *brk)
search for the first occurrence in str of any character in brk

char *strstr(const char *str,
              const char *substr)
search for the first occurrence in str of string substr

char *strerror(int errnum) get the error description for the error number

char *strtok(char *str,
              const char *delimit)
parse tokens from str delimited by delimit

ctype.h

Syntax Description

int isdigit(int c) is digit

int isalpha(int c) is letter

int isalnum(int c) is letter or digit

int iscntrl(int c) is control character

int isgraph(int c) is any character except space

int isprint(int c) is any character or space

int ispunct(int c) is punctuation character

int isspace(int c) is space (space/tab/CR/newline...)

int isxdigit(int c) is hex digit - a..f or A..F

int islower(int c) is lower case letter

int isupper(int c) is upper case letter

int tolower(int c) convert to lower case

int toupper(int c) convert to upper case

math.h

Syntax Description

double pow(double x, double y) power: x^y

double sqrt(double x) square root

double log(double x) natural logarithm: ln(x)

double log10(double x) base 10 logarithm: log₁₀x

double exp(double x) exponent: e^x

double ldexp(double x, int exp) return x*2^exp

double frexp(double x, int *exp) converts x to frac*2^(*exp)

double modf(double x, double *intptr) convert to integer and fraction

double fmod(double x, double y) reminder of x/y

double floor(double x) largest integer that is smaller than x

double ceil(double x) smallest integer that is greater than x

double fabs(double x) float absolute: |x|

double sin(double x) sine of angle [radian]

double cos(double x) cosine of angle [radian]

double tan(double x) tangent of angle [radian]

double asin(double x) arcsine

double acos(double x) arccosine

double atan(double x) arctangent

double atan2(double y, double x) arctangent of y/x

double sinh(double x) hyperbolic sine

double cosh(double x) hyperbolic cosine

double tanh(double x) hyperbolic tangent

fopen mode

mode description

"r" open text file for reading

"w" open/create empty text file for writing

"a" open/create text file for writing from the end

"r+" open text file for reading and writing

"w+" open/create empty text file for reading and writing

"a+" open/create empty text file for reading and writing from the end

"rb" open binary file for reading

"wb" open/create empty binary file for writing

"ab" open/create binary file for writing from the end

"r+b" open binary file for reading and writing

"w+b" open/create empty binary file for reading and writing

"a+b" open/create empty binary file for reading and writing from the end

Printf format:

Syntax:

%[flags][width][.percision][length]type

Flags (optional):

flag description

- align left

+ print sign

0 extra zeros padding

space print space before number, when no sign

# other format

Width (optional):

Minimal output characters width.

Percision (optional):

Set the number of digits after the decimal point for number print.

Set the maximum number of characters to be printed for a string print.

Length (optional):

length description

h short / unsigned short

l long / unsigned long

L long double

Type:

type description variable type print format

c unsigned character unsigned char c

d i signed decimal integer int [-]dddddd

u unsigned decimal integer unsigned int dddddd

x unsigned hexadecimal integer - lower case a..f unsigned int hhhhhh

X unsigned hexadecimal integer - upper case A..F unsigned int HHHHHH

o unsigned octal integer unsigned int oooooo

f floating point number double [-]ddd.ddd

e floating point number double [-]ddd.dddedd

E floating point number double [-]ddd.dddEdd

g minimal length format selection: %f or %e double

G minimal length format selection: %f or %E double

p address of pointer void * hhhhhhhh

s print string char *

n argument get the number of characters written by printf int *

% print % %

scanf format

Syntax:

%[*][width][length]type

* (optional):

Suppress assignment. don't store the current input.

Width (optional):

Minimal output characters width.

Length (optional):

length description

h short / unsigned short

l long / unsigned long

L long double

Type:

type description variable type scan format

c character char * c

d signed decimal integer int * [-]dddddd

i signed integer (dec/hex/oct) int *

u unsigned decimal integer unsigned int * dddddd

x unsigned hexadecimal integer int * hhhhhh

o octal integer int * oooooo

f/e/E/g/G floating point number float * [-]ddd.ddd
[-]ddd.dddedd

p address of pointer void * hhhhhhhh

s get string char *

[...] get string until char not in set char *

[^...] get string until char in set char *

n argument get the number of characters read by scanf int *

% % no assignment occures