Placement new and std::nothrow do not work with MemoryLeakDetectorNewMacros.h

[djboni]

Hello, how are you?

I think I have found an interesting bug.

I am trying to use the placement new to construct in a previously allocated buffer.

However the macro #define new new(__FILE__, __LINE__), defined in MemoryLeakDetectorNewMacros.h, seems to break the placement new.

/* file.cpp */
void f()
{
    // Buffer
    unsigned char buff[100];

    // Placement new
    new (buff) int(0);
}

Compiling the code above gives the following error when including MemoryLeakDetectorNewMacros.h.

src/file.cpp:7:10: error: ‘buff’ does not name a type
    4 |     new (buff) int(0);
      |          ^~~~

There is a workaround, which consists of #undef the macro before the placement new.

/* file.cpp */
void f()
{
    // Buffer
    unsigned char buff[100];

    // Workaround
#ifdef new
    #undef new
#endif

    // Placement new
    new (buff) int(0);
}

I hope that we can fix this, since the placement new is important on embedded systems.

If there are any questions, just let me know.

Best regards,

[basvodde]

Hi,

Thanks. This isn't a bug though but it is "by design", unfortunately. It is because the new is macro-replaced to have additional debug info. You can find more about this in the manual at:
https://cpputest.github.io/manual.html#memory_leak_detection

Which also suggests ways to turn this off when undesired.

[djboni]

The same compilation error described above happens if we use std::nothrow with new, to get a NULL pointer instead of throwing an exception.

// No throw new
int *ptr = new (std::nothrow) int;

The memory leak detector still works when using the workaround described above.
However, after the #undef new, the information about the origin of the leak (file and line) is lost.
Here is an example:

     Memory leak(s) found.
-Alloc num (6) Leak size: 4 Allocated at: file.cpp and line: 42. Type: "new"
+Alloc num (6) Leak size: 4 Allocated at: <unknown> and line: 0. Type: "new"
     Memory: <0x607000000100> Content:
     0000: 00 00 00 00                                      |....|
 Total number of leaks:  1

[basvodde]

Yes, same reason. The new macro finds the file and line location, so when undeffing it then it cannot find that anymore.