strtoll() in C – Syntax, Use and Example

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

strtoll() library function

strtoll() library function is used to convert string representation of integer to long long int type. It is defined in stdlib.h header file.

It was added with C11 standard (update your compiler with C11 standard support to use this function).

Syntax of strtoll() function

long long int strtoll(const char* str, char** endPtr, int base);
  • First parameter str is a pointer to constant character. It contains string to be converted to long long int type.
  • Next it accepts pointer to character pointer. On successful conversion endPtr points to first character after number otherwise is set to NULL pointer.
  • Next parameter is base of input string.
  • On success the function returns converted integer as long long int type and sets endPtr to first character after number. On failure it return 0LL and set endPtr to NULL.

Note: strtoll() efficiently handles integer underflows and overflows. It returns LONG_LONG_MIN or LONG_LONG_MAX if underflow or overflow.

Also learn how to find minimum and maximum range of a type?

Example program to use strtoll() function

 * C program to convert string to long long int using strtoll() library function.

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

int main()
    char number[30];
    char* endPtr;

    long long int bigNumber;
    int base;

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

    printf("Enter base: ");
    scanf("%d", &base);

    /* Convert string representation of number to long long */
    bigNumber = strtoll(number, &endPtr, base);

    /* endPtr points to NULL for failed conversion */
        printf("Unable to convert '%s' to base %d.", number, base);
        printf("Converted long long int = %lld\n", bigNumber);

    return 0;


Enter any number: 9223372036854775807
Enter base: 10
Converted long long int = 9223372036854775807

Enter any number: abfcee12
Enter base: 16
Converted long long int = 2885479954

Enter any number: 0776743
Enter base: 8
Converted long long int = 261603

Enter any number: 0111100110
Enter base: 2
Converted long long int = 486

Enter any number: 922337203685477999999999
Enter base: 10
Converted long long int = 9223372036854775807

Enter any number: -922337203685477599999
Enter base: 10
Converted long long int = -9223372036854775808

Enter any number: error
Enter base: 10
Unable to convert 'error' to base 10.

Happy coding 😉

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