Posted By:
4 Jul, 2013 1:31 pm PDT

Predefined libraries in C++

What are predefined libraries? What are the different libraries and their functions which we commonly use?
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Predefined libraries provide macros, type definitions and functions for tasks like string handling, mathematical computations, input/output processing and memory allocation.

Header files and their functions which we commonly use are:                                              

Function name  Description
strcpy(dest_string, src_string); copies one string to another
strcmp(string1, string2); compares two strings and returns 0, +ve or +ve values
strlen(string);

returns the length of the string 

strcat(string1, string2); appends one string with another Function name Description 
abs(int n); returns the absolute value of n. (i.e |n|)
div(dividened, divisor); computes the quotient and remainder of integer division 
exp(int power) returns e^power 
strcat(string1, string2); Concatenates string1 and string2
log(int x); calculates log (base e) x
sqrt(int x); calculates the square root of x
pow(int x,int y); calculates x^y 
ceil(double x); returns nearest integer not less than x
floor(double x); returns nearest integer not greater than x

 

  • Macro Descriptioncin gets input from the user, cout displays output
  • Function Description: fopen opens a file fclose closes a file, fread reads from a file
  • fgets gets a character string from a file stream
  • fputs writes a character string to a file stream
  • getchar reads a character from stdin gets reads a character string
  • putchar writes a character to
  • stdout puts writes a character string
  • scanf reads formatted input from stdin,
  • a file stream or a buffer printf write formatted output to stdout,
  • a file stream or a buffer remove/erases a file,  rename renames a file Function

Description

malloc(); allocates memory free();

deallocates preciously allocated memory

rand(); generates a random number

abort(); causes abnormal termination of the program

exit(); causes normal termination of the program

 

Function Description

time(); returns the current time of the system

clock(); returns raw processor clock time

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