check the given string is numeric or not.

Applications Programming
1

Hi,

how to check the given string is numeric or not , without converting ( using strtol...).

for ex: if string is C01 - non-numeric data
if string is 001 - numeric data

TIA

2

You are trying with following standard C library function:

This function test only for decimal-digit character
http://www.freebsd.org/cgi/man.cgi?query=isdigit&sektion=3&apropos=0&manpath=FreeBSD\+6.2-RELEASE

This function test for hexadecimal-digit character
http://www.freebsd.org/cgi/man.cgi?query=isxdigit&apropos=0&sektion=0&manpath=FreeBSD\+6.2-RELEASE&format=html

Best regards,
Iliyan Varshilov

3

i don't want to check in a loop using isdigit. need something simple.

4

You are trying to solve your validation problem with regular expression library function .
http://www.opengroup.org/onlinepubs/000095399/functions/regcomp.html

Best regards,
Iliyan Varshilov

5

You are posting is a C programming forum and loops are too difficult?

6

You could make your own function:

#include <stdlib.h>

short strchk (char *s) {
	unsigned short r = 0;

	while (*++s) {
		if (isdigit(s)) {
			r = 1;
		} else {
			r = 0;
			break;
		}
	}
	return r;
}

Note that I didn't compile this code, but it should work.

7

That routine does not check the first character of the string...

Try

int is_numeric(const char *p) {
     if (*p) {
          char c;
          while ((c=*p++)) {
                if (!isdigit(c)) return 0;
          }
          return 1;
      }
      return 0;
}
8

Then you need to use a higher level language. C works at a low level - meaning you develop yourself a library of stuff like: a my_isnumeric() function.
Most C programmers have dozens of little functions they keep around just for stuff like this.

9

Thanks for correcting my code.

I'm actually using that function in a project right now, I'm making my own version of a Reverse Polish Nation calculator. But I made one modification:

if (!isdigit(c) && c != '.') return 0;

Now it has support for floating point and double.

10

I just wrote a script that needed to see if a value was numeric. After reading the above thread, I discovered a simpler way: exploit 'test':

The working code is embedded in a Makefile:
STATUS := $(shell echo `test $${PICTOOLSDEBUG:-0} -gt 0` $$?)
ifeq ($(STATUS),0)
else ifeq ($(STATUS),1)
else
$(error PICTOOLSDEBUG is ${PICTOOLSDEBUG}, \
but should be a small non-negative integer)
endif

More succinctly as a sh script this would be

test $Var -gt 0
if [ $? -ge 2 ] ; then ...is not numeric...; else .. is numeric; fi

Fred Hansen

11

Assuming you have the string in a variable A ,

echo $A | egrep "[1]+$"
if [ $? -eq 0 ]
then
echo "$A is numeric"
else
echo "$A is not numeric"
fi

IF clause can be modified to suit your requiremnent !! Hope this helps.

  1. 0-9 ↩︎

12

A bad way to check this is to use expr :slight_smile:
If VAL is the value you want to check ...
[ "X`expr $VAL + 0 2>/dev/null`" != "X" ] || echo "$VAL is not numeric"