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The isinf macro tests an input floating point value for infinity. isinf(\x) returns 1 if x is infinity, -1 if x is negative infinityval) is non-zero if val is an infinity (positive or negative), and 0 otherwise.

isnan tests if an input is NaN. isnan(\xval) is 1 non-zero if x val is a NaN, and 0 otherwise.

If infinity or NaN values are not acceptable inputs in a program, these macros should be used to ensure they are not passed to vulnerable functions.

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The following code was run on 32-bit GNU Linux using the GCC version 3.4.6 compiler. On this platform, FLT_MAX has the value 340282346638528859811704183484516925440.000000. FLT_MIN=-FLT_MAX.

#include <stdio.h>

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

  float val, currentBalance=0;

  scanf("%f", &val);

  currentBalance+=val;

  printf("%f\n", currentBalance);

  return 0;
}

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The following code first validates the input float before using it. The value is tested to ensure that it is neither an infinity nor negative infinity nor a NaN.

float currentBalance; /* User's cash balance */

void doDeposit(){
  float val;

  scanf("%f", &val);

  intif k=(isinf(x);

  if (k==1)val)) {

    /* handle infinity error */

  }

  if (k==-1){

    /* handle negative infinity error */

  }

  if(isnan(val)) /* test NaN */

  {

    /* handle NaN error */

  }

  if (val>=MAX_VALUE-currentBalance) {
    /*Handle range error*/
  }

  currentBalance+=val;
}

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