# Issues in real programs \- what errors are not there in the world\.\.\.

When testing the analyzer PVS\-Studio on one of the projects we found an interesting error\. This error does not refer to the topic of 64\-bits although its consequences are diagnosed as 64\-bit problems\. But this error attracts attention due to its unusual character and we decided to describe it in the blog\.

Here is the code of a program that, as the author had intended, was to print the value of the matrix items into the internal structure\.

```cpp
Matrix3 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]);
```

Of course, this code is incorrect although compiles well\. It seems that the author, while developing the code, had been distracted by work on a project in a different language and therefore confused the syntaxes\. As a result, the expressions of the type "1, 2″ have the value of the subexpression after the last comma according to C\+\+ language rules\. I\.e\. the expression "1, 2″ equals 2\.

As a result, the given code is equivalent to this:

```cpp
Matrix3 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], m[1], m[2],
  m[0], m[1], m[2],
  m[0], m[1], m[2]);
```

Matrix3 class has an overloaded operator \[\] that returns the pointer to float type:

```cpp
inline const float* operator[] (int iRow) const;
```

Of course, it does not matter at all to the function printf what to take as arguments: float or float\*\. The project compiles with the warning level /W3 and the compiler keeps silent when it comes to these suspicious constructs\. To make Visual C\+\+ generate the warning you should raise the warning level up to /W4\. Then you will see the diagnostic warning "warning C4709: comma operator within array index expression"\.

PVS\-Studio analyzer does not like this code too but due to a different reason\. The expression "m\[0\]" has "float \*" type, i\.e\. [memsize\-type](https://pvs-studio.com/en/blog/terms/0030/) and is an argument for the function with a variable number of arguments\. The analyzer considers that this code can potentially contain errors and generates the diagnostic warning "error [V111](https://pvs-studio.com/en/docs/warnings/v111/): Call function 'printf' with variable number of arguments\. Second argument has memsize type\."