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V634. The priority of the '+' operation…
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
Additional information
Contents

V634. The priority of the '+' operation is higher than that of the '<<' operation. It's possible that parentheses should be used in the expression.

Jul 20 2012

The analyzer has detected a potential error occurring because of the addition, subtraction, division and multiplication operations having a higher priority than the shift operation. Programmers often forget about this, which sometimes causes an expression to have quite a different result than they expect.

Consider an example of incorrect code:

int X = 1<<4 + 2;

The programmer most likely expected that the result of shifting '1' by '4' would be added to '2'. But according to operation priorities in C/C++, addition is performed first and shifting is performed after that.

We can recommend you to write parentheses in all expressions containing operators that you use rarely. Even if some of these parentheses turn out to be unnecessary, it's OK. On the other hand, your code will become more readable and comprehensible and less error-prone.

This is the correct code:

int X = (1<<4) + 2;

How to remove a false warning if it is really that very sequence of calculations you intended: addition first, then the shift?

There are 3 ways to do it:

1) The worst way. You can use the "//-V634" comment to suppress the warning in a certain line.

int X = 1<<4 + 2; //-V634

2) You can add additional parentheses:

int X = 1<<(4 + 2);

3) You can specify your intention using blanks:

int X = 1 << 4+2;

References:

This diagnostic is classified as:

You can look at examples of errors detected by the V634 diagnostic.

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