cppreference.com > All C Functions All C Functions
#, ## | manipulate strings
#define | define variables
#error | display an error message
#if, #ifdef, #ifndef, #else, #elif, #endif | conditional operators
#include | insert the contents of another file
#line | set line and file information
#pragma | implementation specific command
#undef | used to undefine variables
Predefined preprocessor variables | miscellaneous preprocessor variables
abort | stops the program
abs | absolute value
acos | arc cosine
asctime | a textual version of the time
asin | arc sine
assert | stops the program if an expression isn't true
atan | arc tangent
atan2 | arc tangent, using signs to determine quadrants
atexit | sets a function to be called when the program exits
atof | converts a string to a double
atoi | converts a string to an integer
atol | converts a string to a long
bsearch | perform a binary search
calloc | allocates and clears a two-dimensional chunk of memory
ceil | the smallest integer not less than a certain value
clearerr | clears errors
clock | returns the amount of time that the program has been running
cos | cosine
cosh | hyperbolic cosine
ctime | returns a specifically formatted version of the time
difftime | the difference between two times
div | returns the quotient and remainder of a division
exit | stop the program
exp | returns "e" raised to a given power
fabs | absolute value for floating-point numbers
fclose | close a file
feof | true if at the end-of-file
ferror | checks for a file error
fflush | writes the contents of the output buffer
fgetc | get a character from a stream
fgetpos | get the file position indicator
fgets | get a string of characters from a stream
floor | returns the largest integer not greater than a given value
fmod | returns the remainder of a division
fopen | open a file
fprintf | print formatted output to a file
fputc | write a character to a file
fputs | write a string to a file
fread | read from a file
free | returns previously allocated memory to the operating system
freopen | open an existing stream with a different name
frexp | decomposes a number into scientific notation
fscanf | read formatted input from a file
fseek | move to a specific location in a file
fsetpos | move to a specific location in a file
ftell | returns the current file position indicator
fwrite | write to a file
getc | read a character from a file
getchar | read a character from STDIN
getenv | get enviornment information about a variable
gets | read a string from STDIN
gmtime | returns a pointer to the current Greenwich Mean Time
isalnum | true if a character is alphanumeric
isalpha | true if a character is alphabetic
iscntrl | true if a character is a control character
isdigit | true if a character is a digit
isgraph | true if a character is a graphical character
islower | true if a character is lowercase
isprint | true if a character is a printing character
ispunct | true if a character is punctuation
isspace | true if a character is a space character
isupper | true if a character is an uppercase character
isxdigit | true if a character is a hexidecimal character
labs | absolute value for long integers
ldexp | computes a number in scientific notation
ldiv | returns the quotient and remainder of a division, in long integer form
localtime | returns a pointer to the current time
log | natural logarithm
log10 | natural logarithm, in base 10
longjmp | start execution at a certain point in the program
malloc | allocates memory
memchr | searches an array for the first occurance of a character
memcmp | compares two buffers
memcpy | copies one buffer to another
memmove | moves one buffer to another
memset | fills a buffer with a character
mktime | returns the calendar version of a given time
modf | decomposes a number into integer and fractional parts
perror | displays a string version of the current error to STDERR
pow | returns a given number raised to another number
printf | write formatted output to STDOUT
putc | write a character to a stream
putchar | write a character to STDOUT
puts | write a string to STDOUT
qsort | perform a quicksort
raise | send a signal to the program
rand | returns a pseudorandom number
realloc | changes the size of previously allocated memory
remove | erase a file
rename | rename a file
rewind | move the file position indicator to the beginning of a file
scanf | read formatted input from STDIN
setbuf | set the buffer for a specific stream
setjmp | set execution to start at a certain point
setlocale | sets the current locale
setvbuf | set the buffer and size for a specific stream
signal | register a function as a signal handler
sin | sine
sinh | hyperbolic sine
sprintf | write formatted output to a buffer
sqrt | square root
srand | initialize the random number generator
sscanf | read formatted input from a buffer
strcat | concatenates two strings
strchr | finds the first occurance of a character in a string
strcmp | compares two strings
strcoll | compares two strings in accordance to the current locale
strcpy | copies one string to another
strcspn | searches one string for any characters in another
strerror | returns a text version of a given error code
strftime | returns individual elements of the date and time
strlen | returns the length of a given string
strncat | concatenates a certain amount of characters of two strings
strncmp | compares a certain amount of characters of two strings
strncpy | copies a certain amount of characters from one string to another
strpbrk | finds the first location of any character in one string, in another string
strrchr | finds the last occurance of a character in a string
strspn | returns the length of a substring of characters of a string
strstr | finds the first occurance of a substring of characters
strtod | converts a string to a double
strtok | finds the next token in a string
strtol | converts a string to a long
strtoul | converts a string to an unsigned long
strxfrm | converts a substring so that it can be used by string comparison functions
system | perform a system call
tan | tangent
tanh | hyperbolic tangent
time | returns the current calendar time of the system
tmpfile | return a pointer to a temporary file
tmpnam | return a unique filename
tolower | converts a character to lowercase
toupper | converts a character to uppercase
ungetc | puts a character back into a stream
va_arg | use variable length parameter lists
vprintf, vfprintf, and vsprintf | write formatted output with variable argument lists