atoll() in C – Syntax, Use and Example

Write a C program to input string from user and convert string to long long using atoll() library function. How to convert string to long long int type using atoll() library function in C programming?

atoll() library function

atoll() function converts string representation of integer to long long type. It is defined in stdlib.h header file.

It is a part of C11 standard. Therefore, you must have C11 supported compiler installed to use this function.

Syntax of atoll() function

long long int atoll(const char* str);
  • It accepts a pointer to constant character str. Which points to string representation of integer.
  • On success it return converted integer as long long int type. On failure it return 0LL.

Note: The function behaviour is undefined if given integer underflows or overflows long long range. To handle such situations use more reliable and cross-platform strtoll() library function.

Example program to use atoll() function

/**
 * C program to convert string to long long using atoll() library function. 
 */

#include <stdio.h>
#include <stdlib.h>     // Used for atoll()


int main()
{
    char number[30];
    long long int bigNum;


    /* Input string representation of integer from user. */
    printf("Enter any integer: ");
    fgets(number, 30, stdin);


    /* Convert string representation of number to integer */
    bigNum = atoll(number);


    /* Use %lld or %lli to print long long type */
    printf("Converted long long int = %lld\n", bigNum);


    return 0;
}

Output

Enter any integer: 9223372036854775807
Converted long long int = 9223372036854775807

Enter any integer: -9223372036854775808
Converted long long int = -9223372036854775808

Enter any integer: 922337203685477580799
Converted long long int = 9223372036854775807

Enter any integer: -922337203685477580899999999
Converted long long int = -9223372036854775808

Enter any integer: 2018
Converted long long int = 2018

Enter any integer: error
Converted long long int = 0

Happy coding 😉

About Pankaj

Pankaj Prakash is the founder, editor and blogger at Codeforwin. He loves to learn new techs and write programming articles especially for beginners. He works at Vasudhaika Software Sols as a Software Design Engineer and manages Codeforwin. In short Pankaj is Web developer, Blogger, Learner, Tech and Music lover.

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