C Language: strtol function
(Convert String to Long Integer)
In the C Programming Language, the strtol function converts a string to a long integer.
The strtol function skips all white-space characters at the beginning of the string, converts the subsequent characters as part of the number, and then stops when it encounters the first character that isn't a number.
Syntax
The syntax for the strtol function in the C Language is:
long int strtol(const char *nptr, char **endptr, int base);
Parameters or Arguments
- nptr
- A pointer to a string to convert to a long integer.
- endptr
- It is used by the strtol function to indicate where the conversion stopped. The strtol function will modify endptr (if endptr is not a null pointer) so that endptr points to the first character that was not converted.
- base
- The base of the number being converted. If base is between 2 and 36, it is used as the radix of the number. If base is zero, the number is assumed to be decimal unless the converted number starts with O (for Octal), Ox (for hex) or OX (for hex).
Returns
The strtol function returns the long integer representation of a string. The strtol function skips all white-space characters at the beginning of the string, converts the subsequent characters as part of the number, and then stops when it encounters the first character that isn't a number.
If the strtol function converts a value that is too large or too small to convert, it will store ERANGE in errno. If the value is too large to convert, the function will return a value of LONG_MAX. If the value is too small to convert the function will return a value of LONG_MIN.
Required Header
In the C Language, the required header for the strtol function is:
#include <stdlib.h>
Applies To
In the C Language, the strtol function can be used in the following versions:
- ANSI/ISO 9899-1990
strtol Example
Let's look at an example to see how you would use the strtol function in a C program:
/* Example using strtol by TechOnTheNet.com */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <limits.h> int main(int argc, const char * argv[]) { /* Define temporary variables */ char value[10]; char *eptr; long result; /* Copy a value into the variable */ /* It's okay to have whitespace before the number */ strcpy(value, " 123"); /* Convert the provided value to a decimal long */ result = strtol(value, &eptr, 10); /* If the result is 0, test for an error */ if (result == 0) { /* If a conversion error occurred, display a message and exit */ if (errno == EINVAL) { printf("Conversion error occurred: %d\n", errno); exit(0); } } /* If the result is equal to LONG_MIN or LONG_MAX, test for a range error */ if (result == LONG_MIN || result == LONG_MAX) { /* If the value provided was out of range, display a warning message */ if (errno == ERANGE) printf("The value provided was out of range\n"); } /* Display the converted result */ printf("%ld decimal\n", result); /* Copy a hexadecimal value into the variable */ strcpy(value, "0x19e"); /* Convert the provided value to a decimal long */ result = strtol(value, &eptr, 16); /* If the result is 0, test for an error */ if (result == 0) { /* If a conversion error occurred, display a message and exit */ if (errno == EINVAL) { printf("Conversion error occurred: %d\n", errno); exit(0); } } /* If the result is equal to LONG_MIN or LONG_MAX, test for a range error */ if (result == LONG_MIN || result == LONG_MAX) { /* If the value provided was out of range, display a warning message */ if (errno == ERANGE) printf("The value provided was out of range\n"); } /* Display the converted result */ printf("%lx hexadecimal\n", result); return 0; }
When compiled and run, this application will output:
123 decimal 19e hexadecimal
Similar Functions
Other C functions that are similar to the strtol function:
- atoi function <stdlib.h>
- atol function <stdlib.h>
- strtod function <stdlib.h>
- strtoll function <stdlib.h>
- strtoul function <stdlib.h>
See Also
Other C functions that are noteworthy when dealing with the strtol function:
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