# V520. Comma operator ',' in array index expression.

The analyzer found a potential error that may be caused by a misprint. An expression containing the ',' operator is used as an index for an array.

Here is a sample of suspicious code:

    float **array_2D;
    array_2D[getx() , gety()] = 0;

Most probably, it was meant to be:

    array_2D[ getx() ][ gety() ] = 0;

Such errors might appear if the programmer worked earlier with a programming language where array indexes are separated by commas.

Let's look at a sample of an error found by the analyzer in one project:

    float **m;
    TextOutput &t = ...
    ...
    t.printf("%10.5f, %10.5f, %10.5f,\n%10.5f, %10.5f, %10.5f,\n%10.5f,
      %10.5f, %10.5f)",
        m[0, 0], m[0, 1], m[0, 2],
        m[1, 0], m[1, 1], m[1, 2],
        m[2, 0], m[2, 1], m[2, 2]);

Since the printf function of the TextOutput class works with a variable number of arguments, it cannot check whether pointers will be passed to it instead of values of the float type. As a result, we will get rubbish displayed instead of matrix items' values. This is the correct code:

    t.printf("%10.5f, %10.5f, %10.5f,\n%10.5f, %10.5f, %10.5f,\n%10.5f,
      %10.5f, %10.5f)",
        m[0][0], m[0][1], m[0][2],
        m[1][0], m[1][1], m[1][2],
        m[2][0], m[2][1], m[2][2]);

This diagnostic is classified as:

CWE-480 CERT-EXP08-C

You can look at examples of errors detected by the V520 diagnostic.