C Data Type Functions - C atoll

Convert string to long long integer


long long int atoll ( const char * str );


This function has the following parameter.

C-string containing the representation of an integral number.


The function returns the converted integral number as a long long int value.

If no valid conversion could be performed, a zero value is returned.

If the converted value would be out of the range of representable values by a long long int, it causes undefined behavior.


#include <stdio.h> /* printf, fgets */
#include <stdlib.h> /* atoll */
/*from   w  w  w .  j ava2 s .  c o  m*/
int main (){
  long long int lli;
  char buffer[256];
  printf ("Enter a long number: ");
  fgets (buffer, 256, stdin);
  lli = atoll(buffer);
  printf ("The value entered is %lld. Its double is %lld.\n",lli,lli*2);
  return 0;


The code above generates the following result.