atoll() Function

The atoll() function in C converts a numeric string into a long long integer value. It interprets the contents of a string as an integral number and returns the corresponding long long integer.

Syntax of atoll()

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long long int atoll(const char *str);

Parameters

ParameterDescription
strC-string containing the representation of an integral number.

This function behaves similarly to atol() but returns a value of type long long int, allowing it to handle larger numbers. If the string does not represent a valid number, the function returns 0. Moreover, if the numeric value exceeds the representable range of a long long int, the behavior is undefined. For better error handling in such cases, consider using strtoll().

Return Value

On success, the function returns the converted integral number as a long long int. If no valid conversion can be performed, it returns 0.

Exceptions

If the converted value exceeds the range of a long long int, the behavior is undefined. In such cases, using strtoll() is recommended for robust error handling.

Examples for atoll()

Example: Converting a Simple Numeric String

This example demonstrates how to convert a basic numeric string into a long long integer using atoll().

Program

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

int main() {
    const char *numStr = "1234567890";
    long long int num = atoll(numStr);
    printf("Converted number: %lld\n", num);
    return 0;
}

Explanation:

  1. The program defines a string representing a numeric value.
  2. atoll() converts this string into a long long integer.
  3. The converted number is then printed, demonstrating the successful conversion.

Output:

Converted number: 1234567890

Example: Handling an Invalid Numeric String

This example illustrates the behavior of atoll() when the input string does not start with a valid numeric representation.

Program

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

int main() {
    const char *numStr = "abc123";
    long long int num = atoll(numStr);
    printf("Converted number: %lld\n", num);
    return 0;
}

Explanation:

  1. The program defines a string that begins with non-numeric characters.
  2. atoll() attempts to convert the string, but since the initial characters are not numeric, it returns 0.
  3. This result is printed, demonstrating how the function handles invalid input.

Output:

Converted number: 0

Example: Converting a Large Numeric String Within Range

This example demonstrates converting a string representing a large number that is within the representable range of a long long int.

Program

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

int main() {
    const char *numStr = "9223372036854775807";
    long long int num = atoll(numStr);
    printf("Converted number: %lld\n", num);
    return 0;
}

Explanation:

  1. The program defines a string representing the maximum value for a long long int.
  2. atoll() converts the string to a long long int value.
  3. The program prints the converted value, showing that large numbers within the valid range are correctly handled.

Output:

Converted number: 9223372036854775807