Float division by zero

Dividing floating point number by zero

Description

This defect occurs when the denominator of a division operation can be a zero-valued floating point number.

Risk

A division by zero can result in a program crash.

Fix

The fix depends on the root cause of the defect. Often the result details show a sequence of events that led to the defect. Use this event list to determine how the denominator variable acquires a zero value. You can implement the fix on any event in the sequence. If the result details do not show the event history, you can trace back using right-click options in the source code and see previous related events. See also Interpret Bug Finder Results in Polyspace Desktop User Interface.

It is a good practice to check for zero values of a denominator before division and handle the error. Instead of performing the division directly:

res = num/den;

use a library function that handles zero values of the denominator before performing the division:

res = div(num, den);

See examples of fixes below.

If you do not want to fix the issue, for instance, when you handle infinities in your code, add comments to your result or code to avoid another review. See Address Polyspace Results Through Bug Fixes or Justifications.

Examples

Dividing a Floating Point Number by Zero

float fraction(float num)
{
    float denom = 0.0;
    float result = 0.0;

    result = num/denom;

    return result;
}

A division by zero error occurs at num/denom because denom is zero.

Correction — Check Before Division

float fraction(float num)
{
    float denom = 0.0;
    float result = 0.0;

    if( ((int)denom) != 0)
        result = num/denom;

    return result;
}

Before dividing, add a test to see if the denominator is zero, checking before division occurs. If denom is always zero, this correction can produce a dead code defect in your Polyspace^® results.

Correction — Change Denominator

One possible correction is to change the denominator value so that denom is not zero.

float fraction(float num)
{
    float denom = 2.0;
    float result = 0.0;

    result = num/denom;

    return result;
}

Result Information

Group: Numerical

Language: C | C++

Default: On

Command-Line Syntax: FLOAT_ZERO_DIV

Impact: High

CWE ID: 189, 369