C Functions

abort generate an abnormal process abort
abs return an integer absolute value
acos arc cosine function
asin arc sine function
atan arc tangent function
atan2 arc tangent function
atof convert a string to double-precision number
atoi convert a string to integer
atol convert a string to long integer
bsearch binary search a sorted table
calloc a memory allocator
ceil ceiling value function
clearerr clear indicators on a stream
clock report CPU time used
cos cosine function
ctime, ctime_r convert a time value to date and time string
div compute the quotient and remainder of an integer division
ecvt, fcvt, gcvt convert a floating-point number to a string
exit, _exit terminate a process
exp exponential function
fabs absolute value function
fclose close a stream
fcvt convert a floating-point number to a string
fdopen associate a stream with a file descriptor
feof test end-of-file indicator on a stream
ferror test error indicator on a stream
fflush flush a stream
fgetc get a byte from a stream
fgetpos get current file position information
fgets get a string from a stream
fileno map a stream pointer to a file descriptor
floor floor function
fmod floating-point remainder value function
fopen open a stream
fprintf, printf, snprintf, sprintf print formatted output
fputc put a byte on a stream
fputs put a string on a stream
fread binary input
free free allocated memory
freopen open a stream
frexp extract mantissa and exponent from a double precision number
fscanf, scanf, sscanf convert formatted input
fseek, fseeko reposition a file-position indicator in a stream
fsetpos set current file position
ftell, ftello return a file offset in a stream
fwrite binary output
gcvt convert a floating-point number to a string
getc get a byte from a stream
getchar get a byte from a stdin stream
getenv get value of an environment variable
gets get a string from a stdin stream
getw get a word from a stream
hypot Euclidean distance function
index character string operations
initstate, random, setstate, srandom pseudorandom number functions
isalnum test for an alphanumeric character
isalpha test for an alphabetic character
isascii test for a 7-bit US-ASCII character
iscntrl test for a control character
isdigit test for a decimal digit
isgraph test for a visible character
islower test for a lower-case letter
isprint test for a printing character
ispunct test for a punctuation character
isspace test for a white-space character
isupper test for an upper-case letter
isxdigit test for a hexadecimal digit
labs return a long integer absolute value
ldexp load exponent of a floating point number
ldiv compute quotient and remainder of a long division
lfind find entry in a linear search table
log natural logarithm function
log10 base 10 logarithm function
lsearch, lfind linear search and update
malloc a memory allocator
memccpy copy bytes in memory
memchr find byte in memory
memcmp compare bytes in memory
memcpy copy bytes in memory
memmove copy bytes in memory with overlapping areas
memset set bytes in memory
modf decompose a floating-point number
perror write error messages to standard error
pow power function
fprintf, printf, snprintf, sprintf print formatted output
putc put byte on a stream
putchar put byte on stdout stream
putenv change or add a value to environment
puts put a string on standard output
putw put a word on a stream (LEGACY)
rand, rand_r pseudo-random number generator
random generate pseudorandom number
realloc memory reallocator
remove remove files
rewind reset file position indicator in a stream
rindex character string operations
fscanf, scanf, sscanf convert formatted input
setbuf assign buffering to a stream
setstate switch pseudorandom number generator state arrays
setvbuf assign buffering to a stream
sin sine function
fprintf, printf, snprintf, sprintf print formatted output
sprintf, snprintf print formatted output
sqrt square root function
srand seed simple pseudo-random number generator
srandom seed pseudorandom number generator
sscanf convert formatted input
stderr, stdin, stdout standard I/O streams
stdio.h standard buffered input/output
stdlib.h standard library definitions
strcasecmp, strncasecmp case-insensitive string comparisons
strcat concatenate two strings
strchr string scanning operation
strcmp compare two strings
strcpy copy a string
strcspn get length of a complementary substring
strdup duplicate a string
strerror get error message string
strlen get string length
strncasecmp case-insensitive string comparison
strncat concatenate part of two strings
strncmp compare part of two strings
strncpy copy part of a string
strpbrk scan string for byte
strspn get length of a substring
strstr find a substring
strtod convert string to a double-precision number
strtok, strtok_r split string into tokens
strtol convert string to a long integer
strtoul convert string to an unsigned long
swab swap bytes
system issue a command
tan tangent function
tmpfile create a temporary file
tmpnam create a name for a temporary file
toascii translate integer to a 7-bit ASCII character
tolower transliterate upper-case characters to lower-case
toupper transliterate lower-case characters to upper-case
ungetc push byte back into input stream
vfprintf, vprintf, vsnprintf, vsprintf format output of a stdarg argument list