How to check if a string is an integer 1

[suann]

Hi Guys,

I am new to C programming, How do I check if a string is an integer.

Eg., x="AB123456" -- In my program I want to print this is not an integer but if x="123456" I want to print this is an integer.

Any help greatly appreciated.

Thanks
Suann.

 

[Diancecht]

I'd bet for strtol() function. Here you have an example fo use:

http://www.cplusplus.com/ref/cstdlib/strtol.html

If it's not a number, 0 is returned.

Cheers,
Dian

 

[suann]

Thanks Dian for the quick response. What if I am in the middle of program. I am not reading value from the user input. Ex.,

char *Query;
Query=(char *)malloc(sizeof(char)*500);
strcpy(Query,"AB123456");

Now how do I know whether Query string contains only integers or contains both characters and integers. If it contains only integers I want to take some action or else different action.

Thanks again
Ann

 

[Diancecht]

OK, maybe this is a better example:

http://home.att.net/~jackklein/c/code/strtol.html

You have to take the part of the code you need, and call the strtol function with your Query variable.

Cheers,
Dian

 

[Hammer]

Depending on your exact requirements (which are slightly unclear), strtol() might not do what you need.

You start by saying:
>>How do I check if a string is an integer
and then later say:
>>how do I know whether Query string contains only integers
These are two different requirements.

To achieve the former, you would use strtol() as shown in the last link supplied by Dian.

To achieve the latter, strtol() will not necessarily work, as the data could be any number of bytes in length, and the content may well exceed the value an integer (int) can store (INT_MAX or UINT_MAX, limits.h). Therefore, the validation method would be to walk through the array checking each byte using isdigit() (ctype.h) to determine if it is a numeric. Using this method, you can test any number of bytes.