Menu
×
   ❮   
HTML CSS JAVASCRIPT SQL PYTHON JAVA PHP HOW TO W3.CSS C C++ C# BOOTSTRAP REACT MYSQL JQUERY EXCEL XML DJANGO NUMPY PANDAS NODEJS R TYPESCRIPT ANGULAR GIT POSTGRESQL MONGODB ASP AI GO KOTLIN SASS VUE DSA GEN AI SCIPY AWS CYBERSECURITY DATA SCIENCE
     ❯   

C stdlib atol() Function

❮ C stdlib Library


Example

Read a number from a string:

char str[] = "24 degrees";
long int amount = atol(str);
printf("%ld", amount);
Try it Yourself »

Definition and Usage

The atol() function reads a representation of a whole number from a string and returns its value.

While reading it first skips over any whitespace (spaces, tabs or new lines) and then reads all of the characters until it runs into one which is not part of the number. It will stop reading if it finds a decimal point because it is only expecting a whole number. If the characters it reads do not form a valid number representation then it returns 0.

If the number is too large for the long int data type it will overflow and return unexpected values.

The atol() function is defined in the <stdlib.h> header file.

Tip: If the number is not at the beginning of the string you can use a pointer to a different position in the string. See More Examples below for an example.


Syntax

atol(const char * str);

Parameter Values

Parameter Description
str A string containing a representation of a whole number.

Technical Details

Returns: An long int value containing the number represented by the string.

More Examples

Example

Read a number at a specified position in the string:

char str[] = "Today's temperature is 24 degrees";
long int amount = atol(&str[23]);
printf("%ld", amount);
Try it Yourself »

❮ C stdlib Library

×

Contact Sales

If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail:
sales@w3schools.com

Report Error

If you want to report an error, or if you want to make a suggestion, send us an e-mail:
help@w3schools.com

W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Copyright 1999-2024 by Refsnes Data. All Rights Reserved. W3Schools is Powered by W3.CSS.