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Integer conversion overflow

Overflow when converting between integer types

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Description

This defect occurs when converting an integer to a smaller integer type. If the variable does not have enough bytes to represent the original value, the conversion overflows.

The exact storage allocation for different floating point types depends on your processor. See Target processor type (-target).

Risk

Integer conversion overflows result in undefined behavior.

Fix

The fix depends on the root cause of the defect. Often the result details (or source code tooltips in Polyspace as You Code) show a sequence of events that led to the defect. You can implement the fix on any event in the sequence. If the result details do not show this event history, you can search for previous references of variables relevant to the defect using right-click options in the source code and find related events. See also Interpret Bug Finder Results in Polyspace Desktop User Interface or Interpret Bug Finder Results in Polyspace Access Web Interface (Polyspace Access).

You can fix the defect by:

  • Using a bigger data type for the result of the conversion so that all values can be accommodated.

  • Checking for values that lead to the overflow and performing appropriate error handling.

In general, avoid conversions to smaller integer types.

See examples of fixes below.

If you do not want to fix the issue, add comments to your result or code to avoid another review. See:

Extend Checker

A default Bug Finder analysis might not raise this defect when the input values are unknown and only a subset of inputs cause an issue. To check for defects caused by specific system input values, run a stricter Bug Finder analysis. See Extend Bug Finder Checkers to Find Defects from Specific System Input Values.

Examples

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char convert(void) {

    int num = 1000000;

    return (char)num;
}

In the return statement, the integer variable num is converted to a char. However, an 8-bit or 16-bit character cannot represent 1000000 because it requires at least 20 bits. So the conversion operation overflows.

Correction — Change Conversion Type

One possible correction is to convert to a different integer type that can represent the entire number.

long convert(void) {

    int num = 1000000;

    return (long)num;
}

Result Information

Group: Numerical
Language: C | C++
Default: On
Command-Line Syntax: INT_CONV_OVFL
Impact: High

Version History

Introduced in R2013b

See Also

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