NameDesc
abort()It terminates the C program
abs()This function returns the absolute value of an integer . The absolute value of a number is always positive. Only integer values are supported in C.
asctimeConvert Date and Time to ASCII
asctime()Tm structure contents are interpreted by this function as calendar time. This time is converted into string.
assert()This function gets an integer as paramenter. If this paramenter is 0, writes message to stderr. Then, terminates the program. If this paramenter is non 0, it does nothing.
atexitRegister Function to be Called at Program Exit
atof()Converts string to float
atoi()Converts string to int
atol()Converts string to long
bsearchBinary Search
calloc()This function is also like malloc () function. But calloc () initializes the allocated memory to zero. But, malloc() doesn’t
ceil()This function returns nearest integer value which is greater than or equal to the argument passed to this function.
clearerr()This function clears the error indicators
clock()This function is used to get current system time
clrscr()This function is used to clear the output screen.
cos()This function is used to calculate cosine.
cosh()This function is used to calculate hyperbolic cosine.
ctime()This function is used to return string that contains date and time informations
delay()This function Suspends the execution of the program for particular time
difftime()This function is used to get the difference between two given times
div()This function performs division operation
errno()This function sets errno value to 0 at the beginning of the program. This value is modified to other than 0 when an error occurs while any function call.
exit()This function terminates the program and does not return any value
exp()This function is used to calculate the exponential “e” to the xth power.
fclose()closes an opened file
feof()finds end of file
ferrorTest for File Error
fflush()flushes a file
fgetc()reads a character from file
fgetcharreads a character from keyboard
fgetposGet File Position
fgets()reads string from a file, one line at a time
floor()This function returns the nearest integer which is less than or equal to the argument passed to this function.
fopen()All file handling functions are defined in stdio.h header file
fprintf()writes formatted data to a file
fputc()writes a character to file
fputcharwrites a character from keyboard
fputs()writes string to a file
freadRead Block from File
free()This function frees the allocated memory by malloc (), calloc (), realloc () functions and returns the memory to the system.
freopenReopen File
fscanf()reads formatted data from a file
fseek()moves file pointer position to given location
fsetposSet File Position
ftell()gives current position of file pointer
fwriteWrite Block to File
getc()It reads character from file
getdate()This function is used to get the CPU time
getenv()This function gets the current value of the environment variable
getch()It reads character from keyboard
getchar()It reads character from keyboard
getche()It reads character from keyboard and echoes to o/p screen
gets()It reads line from keyboard
getw()reads an integer from file
gmtime()This function shares the tm structure that contains date and time informations
isalnum()checks whether character is alphanumeric
isalpha()checks whether character is alphabetic
iscntrl()checks whether character is a control character
isdigit()checks whether character is digit
isgraph()checks whether character is a graphical character
islower()checks whether character is lower case
isprint()checks whether character is a printable character
ispunct()checks whether character is a punctuation
isspace()checks whether character is space
isupper()checks whether character is upper case
isxdigit()checks whether character is hexadecimal
labsAbsolute Value of Long Integer
ldivLong Integer Division
localeconv()It gets locale conventions
localtime()This function shares the tm structure that contains date and time informations
log()This function is used to calculates natural logarithm.
log10()This function is used to calculates base 10 logarithm.
longjmp()It is used for non local jump
malloc()This function is used to allocate space in memory during the execution of the program.
mblenCompute Length of Multibyte Character
mbstowcsConvert Multibyte String to Wide Character String
mbtowcConvert Multibyte Character to Wide Character
memcmp()It is used to compare specified number of characters from two buffers
memcpy()It is used to copy a specified number of bytes from one memory to another
memchr()It is used to locate the first occurrence of the character in the specified string
memicmp()It is used to compare specified number of characters from two buffers regardless of the case of the characters
memmoveCopy Memory Block
memmove()It is used to copy a specified number of bytes from one memory to another or to overlap on same memory.
memset()It is used to initialize a specified number of bytes to null or any other value in the buffer
mktime()This function interprets tm structure as calendar time
perror()This function displays most recent error that happened during library function call.
pow()This is used to find the power of the given number.
printf()This function is used to print the character, string, float, integer, octal and hexadecimal values onto the output screen
putc()writes a character to file
putenv()This function modifies the value for environment variable
putchar()It writes a character to screen
puts()It writes line to o/p screen
putw()writes an integer to file
qsortSort Array
raise()It is used to raise signal in a C program
rand()This function returns the random integer numbers
realloc()This function modifies the allocated memory size by malloc () and calloc () functions to new size
remove()s a file
renameRename File
rewind()moves file pointer position to the beginning of the file
round()This function returns the nearest integer value of the float/double/long double argument passed to this function. If decimal value is from ”.1 to .5″, it returns integer value less than the argument. If decimal value is from “.6 to .9″, it returns the integer value greater than the argument.
scanf()This function is used to read a character, string, numeric data from keyboard.
setbufSet Buffer (obsolete)
setdate()This function used to modify the system date
setenv()This function sets the value for environment variable
setjmp()This function prepares to use longjmp() function
setlocale()It sets locale()
setvbufSet Buffer
signal()It is used to install signal handler
sin()This function is used to calculate sine value.
sinh()This function is used to calculate hyperbolic sine.
sprint()writes formatted output to string
sqrt()This function is used to find square root of the argument passed to this function.
srandSeed Pseudo-Random Number Generator
sscanf()Reads formatted input from a string
strcat(str1, str2) Concatenates str2 at the end of str1.
strcmp(str1, str2) Returns 0 if str1 is same as str2. Returns <0 if strl < str2. Returns >0 if str1 > str2.
strcmpi(str1,str2) Same as strcmp() function. But, this function negotiates case. “A” and “a” are treated as same.
strcollString Compare Using Locale-Specific Collating Sequence
strcpy(str1, str2) Copies str2 into str1
strcspnSearch String for Intial Span of Characters Not in Set
strdup() duplicates the string
strerrorConvert Error Number to String
strftime()This function is used to modify the actual time format
strchr(str1,char) Returns pointer to first occurrence of char in str1.
strlen(strl) gives the length of str1.
strlwr() converts string to lowercase
strncat() appends a portion of string to another
strncmpBounded String Compare
strncpy() copies given number of characters of one string to another
strpbrkSearch String for One of a Set of Characters
strrev() reverses the given string
strrchr() last occurrence of given character in a string is found
strset() sets all character in a string to given character
strspnSearch String for Initial Span of Characters in Set
strstr(str1, str2) Returns pointer to first occurrence of str2 in str1.
strtod()Converts string to double
strtok() tokenizing given string using delimiter
strtol()Converts string to long
strtollConvert String to Long Long
strtoulConvert String to Unsigned Long Integer
strupr() converts string to uppercase
strxfrmTransform Locale-Specific String
system()This function is used to execute commands outside the C program.
tan()This function is used to calculate tangent.
tanh()This function is used to calculate hyperbolic tangent.
textbackground()This function is used to change text background
textcolor()This function is used to change the text color
time()This function is used to get current system time as structure
tmpfileCreate Temporary File
tmpnamGenerate Temporary File Name
tolower()checks whether character is alphabetic & converts to lower case
toupper()checks whether character is alphabetic & converts to upper case
trunc()This function truncates the decimal value from floating point value and returns integer value.
ungetcUnread Character
va_arg()This function is used to fetch the arguments from variable length argument list
va_end()This function indicates the end process of variable length argument list in a program
va_start()This function indicates the start process of variable length argument list in a program
vfprintfFormatted File Write Using Variable Argument List
vprintfFormatted Write Using Variable Argument List
vsprintfFormatted String Write Using Variable Argument List
wcstombsConvert Wide Character String to Multibyte String
wctombConvert Wide Character to Multibyte Character

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