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V765. Compound assignment expression 'X…
Analyzer diagnostics
General Analysis (C++)
General Analysis (C#)
General Analysis (Java)
Diagnosis of micro-optimizations (C++)
Diagnosis of 64-bit errors (Viva64, C++)
MISRA errors
AUTOSAR errors
OWASP errors (C#)
Additional information
Contents

V765. Compound assignment expression 'X += X + N' is suspicious. Consider inspecting it for a possible error.

Jul 21 2016

The analyzer detected a potential error in an arithmetic or logical expression: a variable is used both in the left and the right parts of a compound-assignment expression.

Consider the following example:

void Foo(int x, int y, int z)
{
  x += x + y;
  ....
}

This code is likely to contain a typo and was probably meant to look like this:

void Foo(int x, int y, int z)
{
  x = x + y;
  ....
}

Or like this:

void Foo(int x, int y, int z)
{
  x += z + y;
  ....
}

It is true that programmers use expressions like these as a tricky means to multiply a number by two, but such code is strange and needs to be checked. Such expressions look rather complicated and probably should be rewritten in a simpler and clearer way:

void Foo(int x, int y, int z)
{
  x = x * 2 + y;
  ....
}

There are also more suspicious expressions that need to be inspected:

void Foo(int x, int y)
{
  x -= x + y;
}

This expression can be simplified in the following way:

  • x -= x + y;
  • x = x - (x + y);
  • x = -y;

It is not clear if this behavior is intended or caused by a typo. In any case, this code should be checked.

This diagnostic is classified as:

You can look at examples of errors detected by the V765 diagnostic.

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