atol, _atol_l, _wtol, _wtol_l

Article
06/05/2017

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Convert a string to a long integer.

Syntax

long atol(  
   const char *str   
);  
long _atol_l(  
   const char *str,  
   _locale_t locale  
);  
long _wtol(  
   const wchar_t *str   
);  
long _wtol_l(  
   const wchar_t *str,  
   _locale_t locale  
);

Parameters

str
String to be converted.

locale
Locale to use.

Return Value

Each function returns the long value produced by interpreting the input characters as a number. The return value is 0L for atol if the input cannot be converted to a value of that type.

In the case of overflow with large positive integral values, atol returns LONG_MAX; in the case of overflow with large negative integral values, LONG_MIN is returned. In all out-of-range cases, errno is set to ERANGE. If the parameter passed in is NULL, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions set errno to EINVAL and return 0.

Remarks

These functions convert a character string to a long integer value (atol).

The input string is a sequence of characters that can be interpreted as a numerical value of the specified type. The function stops reading the input string at the first character that it cannot recognize as part of a number. This character may be the NULL character ('\0' or L'\0') terminating the string.

The str argument to atol has the following form:

[whitespace] [sign] [digits]]

A whitespace consists of space or tab characters, which are ignored; sign is either plus (+) or minus (–); and digits are one or more digits.

_wtol is identical to atol except that it takes a wide character string.

The versions of these functions with the _l suffix are identical except that they use the locale parameter passed in instead of the current locale. For more information, see Locale.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
`_tstol`	`atol`	`atol`	`_wtol`
`_ttol`	`atol`	`atol`	`_wtol`

Requirements

Routines	Required header
`atol`	<stdlib.h>
`_atol_l`, `_wtol`, `_wtol_l`	<stdlib.h> and <wchar.h>

Example

This program shows how numbers stored as strings can be converted to numeric values using the atol function.

// crt_atol.c  
// This program shows how numbers stored as  
// strings can be converted to numeric values  
// using the atol functions.  
#include <stdlib.h>  
#include <stdio.h>  
#include <errno.h>  
  
int main( void )  
{  
    char    *str = NULL;  
    long    value = 0;  
  
    // An example of the atol function  
    // with leading and trailing white spaces.  
    str = "  -2309 ";  
    value = atol( str );  
    printf( "Function: atol( \"%s\" ) = %d\n", str, value );  
  
    // Another example of the atol function   
    // with an arbitrary decimal point.  
    str = "314127.64";  
    value = atol( str );  
    printf( "Function: atol( \"%s\" ) = %d\n", str, value );  
  
    // Another example of the atol function  
    // with an overflow condition occurring.  
    str = "3336402735171707160320";  
    value = atol( str );  
    printf( "Function: atol( \"%s\" ) = %d\n", str, value );  
    if (errno == ERANGE)  
    {  
       printf("Overflow condition occurred.\n");  
    }  
}

Function: atol( "  -2309 " ) = -2309  
Function: atol( "314127.64" ) = 314127  
Function: atol( "3336402735171707160320" ) = 2147483647  
Overflow condition occurred.