Division and modulo operations are susceptible to divide-by-zero errors.

Division

The result of the / operator is the quotient from the division of the first arithmetic operand by the second arithmetic operand. Division operations are susceptible to divide-by-zero errors. Overflow can also occur during twos-complement signed integer division when the dividend is equal to the minimum (negative) value for the signed integer type and the divisor is equal to -1.

Non-Compliant Code Example

The following code can result in a divide-by-zero error during the division of the signed operands sl1 and sl2.

signed long sl1, sl2, result;

result = sl1 / sl2;

Compliant Solution

The following compliant solution tests the suspect division operation to guarantee there is no possibility of divide-by-zero errors or signed overflow.

signed long sl1, sl2, result;

if ( (sl2 == 0) || ( (sl1 == LONG_MIN) && (sl2 == -1) ) ) {
  /* handle error condition */
}
result = sl1 / sl2;

Modulo

The modulo operator provides the remainder when two operands of integer type are divided.

Non-Compliant Code Example

The following code can result in a divide-by-zero error during the modulo operation on the signed operands sl1 and sl2.

signed long sl1, sl2, result;

result = sl1 % sl2;

Compliant Solution

The following compliant solution tests the suspect modulo operation to guarantee there is no possibility of a divide-by-zero error.

signed long sl1, sl2, result;

if (sl2 == 0) {
  /* handle error condition */
}
result = sl1 % sl2;

Consequences

Divide-by-zero errors can lead to abnormal program termination and denial-of-service attacks.

References

• ISO/IEC 9899-1999 6.5.5 Multiplicative operators
• Seacord 05 Chapter 5 Integers
• Warren 02 Chapter 2 Basics