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The C ISO Standard defines octal constants as a 0 followed by octal digits (0 1 2 3 4 5 6 7).

This can lead to programming errors in constants that are meant to be taken by their decimal value, especially when declaring multiple constants and preserving fixed length.

Example

When declaring integer constants as in:

Programming errors can occur when decimal values are mistakenly specified as octal constants.

Noncompliant Code Example

In this noncompliant code example, a decimal constant is mistakenly prefaced with zeros so that all the constants are a fixed length:

i_array[0] = 2192719;
i_array[1] = 042;

The constant

042

is interpreted as octal, with decimal value

34

Which might or might not be what the programmer wanted.

Risk assesment

4435;
i_array[2] = 0042;

Although it may appear that i_array[2] is assigned the decimal value 42, it is actually assigned the decimal value 34.

Compliant Solution

To avoid using wrong values and to make the code more readable, do not preface constants with zeroes if the value is meant to be decimal:

i_array[0] = 2719;
i_array[1] = 4435;
i_array[2] =   42;

Risk Assessment

Misrepresenting decimal values as octal can lead to incorrect comparisons and assignmentsMisinterpreting decimal values as octal could lead to an incorrect value being written into code.

References

Automated Detection

Related Guidelines

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Image Added Image Added Image Added Wiki Markup\[[ISO/IEC 9899:1999|cplusplus:AA. C References#ISO/IEC 9899-1999]\] Section 6.4.4.1 "Integer constants" \[cplusplus:MISRA 04\] Section 6.7 Rule 7.1