# V001. A code fragment from 'file' cannot be analyzed.

The analyzer sometimes fails to diagnose a file with source code completely.

There may be three reasons for that:

1) An error in code

There is a template class or template function with an error. If this function is not instantiated, the compiler fails to detect some errors in it. In other words, such an error does not hamper compilation. PVS-Studio tries to find potential errors even in classes and functions that are not used anywhere. If the analyzer cannot parse some code, it will generate the V001 warning. Consider a code sample:

    template <class T>
    class A
    {
    public:
      void Foo()
      {
        //forget ;
        int x
      }
    };

Visual C++ will compile this code if the A class is not used anywhere. But it contains an error, which hampers PVS-Studio's work.

2) An error in the Visual C++'s preprocessor

The analyzer uses the Visual C++'s preprocessor while working. From time to time this preprocessor makes errors when generating preprocessed "*.i" files. As a result, the analyzer receives incorrect data. Here is a sample:

    hWnd = CreateWindow (
      wndclass.lpszClassName,    // window class name
      __T("NcFTPBatch"),         // window caption
      WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX,
        // window style
      100,            // initial x position
      100,            // initial y position
      450,            // initial x size
      100,            // initial y size
      NULL,           // parent window handle
      NULL,           // window menu handle
      hInstance,      // program instance handle
      NULL);          // creation parameters
    if (hWnd == NULL) {
    ...

Visual C++'s preprocessor turned this code fragment into:

    hWnd = // window class name// window caption// window style//
    initial x position// initial y position// initial x size//
    initial y size// parent window handle// window menu handle//
    program instance handleCreateWindowExA(0L,
    wndclass.lpszClassName, "NcFTPBatch", 0x00000000L | 0x00C00000L |
     0x00080000L | 0x00020000L, 100, 100,450, 100, ((void *)0),
    ((void *)0), hInstance, ((void *)0)); // creation parameters
    if (hWnd == NULL) {
    ...

It turns out that we have the following code:

    hWnd = // a long comment
    if (hWnd == NULL) {
    ...

This code is incorrect and PVS-Studio will inform you about it. Of course it is a defect of PVS-Studio, so we will eliminate it in time.

It is necessary to note that Visual C++ successfully compiles this code because the algorithms it uses for compilation purposes and generation of preprocessed "*.i" files are different.

3) Defects inside PVS-Studio

On rare occasions PVS-Studio fails to parse complex template code.

Whatever the reason for generating the V001 warning, it is not crucial. Usually incomplete parse of a file is not very significant from the viewpoint of analysis. PVS-Studio simply skips a function/class with an error and continues analyzing the file. Only a small code fragment is left unanalyzed.