C strtoll() Function | Convert String to Long Long Integer with Base Support

Introduction

The strtoll() function in C is a standard library function that converts a string to a long long integer. It is part of the C standard library (stdlib.h). This function is more versatile and robust than atoll() because it allows for error checking and supports different number bases.

strtoll() Function Syntax

The syntax for the strtoll() function is as follows:

long long int strtoll(const char *str, char **endptr, int base);

Parameters:

• str: A C string that contains the representation of a long long integer.
• endptr: A pointer to a character pointer. If endptr is not NULL, strtoll() stores the address of the first invalid character in *endptr.
• base: The base of the number represented by str. This can be any value from 2 to 36, or 0 to automatically detect the base.

Returns:

• The function returns the converted long long integer value. If no valid conversion could be performed, it returns 0.

Examples

Converting a Simple String to Long Long Integer

To demonstrate how to use strtoll() to convert a string to a long long integer, we will write a simple program.

Example

#include <stdio.h>
#include <stdlib.h>

int main() {
    const char *str = "123456789012345";
    char *endptr;
    long long int num;

    // Convert string to long long integer
    num = strtoll(str, &endptr, 10);

    // Print the converted value
    printf("The converted value is: %lld\n", num);

    // Print the remaining part of the string
    if (*endptr != '\0') {
        printf("Remaining part of the string: %s\n", endptr);
    }

    return 0;
}

Output:

The converted value is: 123456789012345

Handling Invalid Input

This example shows how strtoll() behaves with invalid input.

Example

#include <stdio.h>
#include <stdlib.h>

int main() {
    const char *str = "abc1234567890";
    char *endptr;
    long long int num;

    // Convert string to long long integer
    num = strtoll(str, &endptr, 10);

    // Print the converted value
    printf("The converted value is: %lld\n", num);

    // Print the remaining part of the string
    if (*endptr != '\0') {
        printf("Remaining part of the string: %s\n", endptr);
    }

    return 0;
}

Output:

The converted value is: 0
Remaining part of the string: abc1234567890

Converting Strings with Different Bases

This example shows how strtoll() can be used to convert strings with different number bases.

Example

#include <stdio.h>
#include <stdlib.h>

int main() {
    const char *str = "1A3F";
    char *endptr;
    long long int num;

    // Convert hexadecimal string to long long integer
    num = strtoll(str, &endptr, 16);

    // Print the converted value
    printf("The converted value is: %lld\n", num);

    // Print the remaining part of the string
    if (*endptr != '\0') {
        printf("Remaining part of the string: %s\n", endptr);
    }

    return 0;
}

Output:

The converted value is: 6719

Real-World Use Case

Converting User Input to Long Long Integer with Error Checking

In real-world applications, the strtoll() function can be used to convert user input, provided as a string, into a long long integer with proper error checking.

Example

#include <stdio.h>
#include <stdlib.h>

int main() {
    char input[100];
    char *endptr;
    long long int value;

    // Prompt the user for input
    printf("Enter a long long integer: ");
    fgets(input, sizeof(input), stdin);

    // Convert input to long long integer
    value = strtoll(input, &endptr, 10);

    // Check for errors
    if (endptr == input) {
        printf("No valid conversion could be performed.\n");
    } else {
        // Print the converted value
        printf("You entered: %lld\n", value);

        // Print the remaining part of the string
        if (*endptr != '\0' && *endptr != '\n') {
            printf("Remaining part of the string: %s\n", endptr);
        }
    }

    return 0;
}

Output (example user input "1234567890123456789abc"):

Enter a long long integer: 1234567890123456789abc
You entered: 1234567890123456789
Remaining part of the string: abc

Conclusion

The strtoll() function is used for converting strings to long long integer values in C. It allows for precise and reliable conversion of numerical data stored as strings, with the added benefit of error handling and support for different number bases. Always handle invalid input scenarios to ensure robust applications.