C stdlib atol() Function
Example
Read a number from a string:
char str[] = "24 degrees";
long int amount = atol(str);
printf("%ld", amount);
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);