check if input is a valid float number 2

[praywin]

Hi,
I want to check if the input is a valid float number. i.e. it should filter out 12..0 , abc , 12abc etc. I was trying to read in the input as a string but it didn't work that great. Please let me know if you know of some other way.
Cheers,
Pravin.

 

[dchoulette]

Read the input in a string then convert it with strtod and check if the endptr arg of strtod points to the end of string ('\0' char).

For more info:

man strtod

Denis

 

[praywin]

Thanks.
I used

num=strtol(input,&endptr,0);
if (endptr!=\'0') {
// number is valid
} else {
//number is invalid
}

but it doesn't work. It gives the same result for any input.

 

[dchoulette]

Use strtod (for double values) not strtol (for long values).

Do not check if endptr is null but if it points to a null character.

Furthermore, endptr points to the first invalid character, so if endptr points to a null char the number is valid.

Note that if you read from a file, endptr could points to a '\n' character instead of '\0', meaning that your number is followed by an end-of-line.

The following code is an example:

#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char *argv[])
{
  char input[256];

  while ((void)fprintf(stdout, &quot;Enter a float number :&quot;),
	 fgets(input, sizeof(input), stdin) != (char *)(NULL))
    {
      char   *endptr;
      double value = strtod(input, &endptr);

      if ((endptr[0] == '\0') || (endptr[0] == '\n'))
	(void)fprintf(stdout, &quot;Double number read : %lf\n&quot;, value);
      else
	(void)fprintf(stdout, &quot;garbage characters found: %s\n&quot;, endptr);
    }
  return 0;
}

"When all else has failed, read the manuals."

Denis

 

[praywin]

Thanks