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C stdlib atoi() Function

❮ C stdlib Library


Example

Read a number from a string:

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

Definition and Usage

The atoi() 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 int data type it will overflow and return unexpected values.

The atoi() 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

atoi(const char * str);

Parameter Values

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

Technical Details

Returns: An 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";
int amount = atoi(&str[23]);
printf("%d", amount);
Try it Yourself »

❮ C stdlib Library

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