strtol, strtoll

Defined in header `<stdlib.h>`
long strtol( const char str, char *str_end, int base );		(until C99)
long strtol( const char restrict str, char *restrict str_end, int base );		(since C99)
long long strtoll( const char restrict str, char *restrict str_end, int base );		(since C99)

Interprets an integer value in a byte string pointed to by str.

Function discards any whitespace characters (as identified by calling isspace()) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid base-n (where n=base) integer number representation and converts them to an integer value. The valid integer value consists of the following parts:

(optional) plus or minus sign
(optional) prefix (0) indicating octal base (applies only when the base is 8 or 0)
(optional) prefix (0x or 0X) indicating hexadecimal base (applies only when the base is 16 or 0)
a sequence of digits

The set of valid digits for base-2 integer is 01, for base-3 integer is 012, and so on. For bases larger than 10, valid digits include alphabetic characters, starting from Aa for base-11 integer, to Zz for base-36 integer. The case of the characters is ignored.

Additional numeric formats may be accepted by the currently installed C locale.

If the value of base is 0, the numeric base is auto-detected: if the prefix is 0, the base is octal, if the prefix is 0x or 0X, the base is hexadecimal, otherwise the base is decimal.

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is NULL, it is ignored.

If the str is empty or does not have the expected form, no conversion is performed, and (if str_end is not NULL) the value of str is stored in the object pointed to by str_end.

If successful, an integer value corresponding to the contents of str is returned.
If the converted value falls out of range of corresponding return type, a range error occurs (setting errno to ERANGE) and LONG_MAX, LONG_MIN, LLONG_MAX or LLONG_MIN is returned.
If no conversion can be performed, 0 is returned.

[edit] Example

Run this code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
 
int main(void)
{
    char str[] = "Is 0xff bigger than 0 or 0x00? The answer is 42.";
    int i = 0;
    int len = strlen(str);
    char *num;
 
    while (i < len) {
        long found = strtol(&str[i], &num, 0);
 
        if (errno) {
            perror("Error");
            exit(EXIT_FAILURE);
        } else if (found || num != &str[i]) {
            printf("Found %li at position %d\n", found, i);
            i = num - str;
        } else {
            i++;
        }
    }
 
    /* Base 36 */
    printf("\n%ld\n", strtol("XyZ",NULL,36));
 
    /* Overflow (range error) */
    errno = 0;
    printf("%ld\n", strtol("9223372036854775808",NULL,10));   // LONG_MAX+1 --> LONG_MAX
    printf("%s\n",strerror(errno));                           // range error
 
    return 0;
}

Output:

Found 255 at position 2
Found 0 at position 19
Found 0 at position 24
Found 42 at position 44
 
44027
9223372036854775807
Numerical result out of range

[edit] See also

atoiatolatoll	converts a byte string to an integer value (function)
strtoul strtoull	converts a byte string to an unsigned integer value (function)
C++ documentation for strtol, strtoll

Language
Standard Library
Type support
Dynamic memory management
Error handling
Program utilities
Date and time utilities
Strings library
Algorithms
Numerics
Input/output support
Localization support
Thread support (C11)
Atomic operations (C11)

strtol, strtoll

Contents

[edit] Parameters

[edit] Return value

[edit] Example

[edit] See also

str	-	pointer to the null-terminated byte string to be interpreted
str_end	-	pointer to a pointer to character.
base	-	base of the interpreted integer value