strtoll() Function

The strtoll() function is declared in the header file <stdlib.h>.

The strtoll() function converts a string representation of an integral number into a value of type long long int. It interprets the input string based on the specified numerical base and can provide a pointer to the character where the conversion stopped, enabling further processing of the string.

Syntax of strtoll()

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

Parameters

ParameterDescription
strA C-string that begins with the representation of an integral number.
endptrA pointer to a pointer of char. After conversion, it is set to point to the character in str immediately after the numerical value. It can be NULL if this information is not needed.
baseAn integer representing the numerical base (radix) for conversion. If this is 0, the base is determined automatically based on the format of str.

It is worth noting that strtoll() behaves similarly to strtol(), but it supports conversion into a larger integer type. The function handles various bases and can indicate conversion errors, such as out-of-range values or the absence of any valid conversion.

Return Value

On success, strtoll() returns the converted value as a long long int. If no valid conversion is performed, it returns 0LL. In cases where the converted value is outside the range of representable values, LLONG_MAX or LLONG_MIN is returned, and errno is set to ERANGE.

Examples for strtoll()

Example 1: Basic Decimal Conversion

This example demonstrates a simple conversion of a decimal string into a long long int using base 10.

Program

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

int main() {
    const char *numStr = "1234567890123";
    char *end;
    long long int num = strtoll(numStr, &end, 10);

    printf("Converted number: %lld\n", num);
    return 0;
}

Explanation:

  1. A string "1234567890123" is defined.
  2. strtoll() converts this string to a long long int using base 10.
  3. The result is stored in the variable num and printed.

Program Output:

Converted number: 1234567890123

Example 2: Hexadecimal Conversion

This example converts a hexadecimal string into a long long int by specifying base 16.

Program

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

int main() {
    const char *hexStr = "0x1A3F";
    char *end;
    long long int num = strtoll(hexStr, &end, 16);

    printf("Converted hexadecimal: %lld\n", num);
    return 0;
}

Explanation:

  1. A hexadecimal string "0x1A3F" is defined.
  2. strtoll() is called with base 16 to convert the string.
  3. The resulting number is printed as a long long int.

Program Output:

Converted hexadecimal: 6719

Example 3: Using endptr to Determine Conversion Stop Point

This example illustrates how to use the endptr parameter to determine where the numerical conversion stopped in the input string.

Program

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

int main() {
    const char *inputStr = "789xyz";
    char *end;
    long long int num = strtoll(inputStr, &end, 10);

    printf("Converted number: %lld\n", num);
    printf("Remaining string: %s\n", end);
    return 0;
}

Explanation:

  1. The string "789xyz" contains a valid number followed by non-numeric characters.
  2. strtoll() converts the numeric portion "789" into a long long int.
  3. The pointer end is set to the beginning of the remaining non-numeric characters ("xyz"), which is then printed.

Program Output:

Converted number: 789
Remaining string: xyz

Example 4: Handling Invalid Conversion and Range Errors

This example demonstrates how strtoll() handles a case where no valid conversion occurs and where the converted value exceeds the representable range.

Program

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

int main() {
    const char *invalidStr = "not_a_number";
    char *end;
    errno = 0;
    long long int num = strtoll(invalidStr, &end, 10);

    if (invalidStr == end) {
        printf("No valid conversion could be performed.\n");
    } else if (errno == ERANGE) {
        printf("The number is out of range.\n");
    } else {
        printf("Converted number: %lld\n", num);
    }
    return 0;
}

Explanation:

  1. An input string "not_a_number" that does not start with a valid numeric representation is defined.
  2. strtoll() fails to perform a conversion, and the end pointer remains at the start of the string.
  3. The program checks if no conversion occurred and prints an appropriate message.

Program Output:

No valid conversion could be performed.