V651. Suspicious operation of 'sizeof(X)/sizeof(T)' kind, where 'X' is of the 'class' type.

The analyzer has detected a potential error in an expression of the 'sizeof(X)/sizeof(X[0])' kind. The strange thing is that the 'X' object is a class instance.

The 'sizeof(X)/sizeof(X[0]) ' is usually used to calculate the number of items in the 'X' array. The error might occur during careless code refactoring. The 'X' variable was an ordinary array at first and was then replaced with a container class, while calculation of the items number remained the same.

Consider an example of incorrect code:

#define countof( x ) (sizeof(x)/sizeof(x[0]))
Container<int, 4> arr;
for( int i = 0; i < countof(arr); i++ )
{ .... }

The programmer expected the code to calculate the number of the items of the 'arr' variable. But the resulting value is the class size divided by the size of the 'int'- variable. Most likely, this value is not in any way related to the number of data items being stored in the container.

This is the fixed code:

const size_t count = 4;
Container<int, count> arr;
for( int i = 0; i < arr.size(); i++ )
{ .... }

This diagnostic is classified as:

CWE-682