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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