String changes after passing by reference

Question

I am writing a simulation project in C++ using Visual Studio 2012 (standard C++ with no /clr support) and I face the following problem. In the code somewhere I pass a string by reference:

theClassObject->Method("12345")

where the definition of the method in the class is:

TheClass::Method(const std::string& STR) {..}

and when I check the value of the STR during debugging it has four more bytes in front, for example "~#.a12345" and the length of the string is increased by these four bytes. In other places of the code with other similar methods this does not happen.

Did I miss some compiler option for the project or there are other reasons I miss?

I am not sure if I provided all the information needed, but I could if needed.

Thanks in advance!

This should not happen. From what you posted, it's pretty much impossible to guess what went wrong. Can you reduce your problem to a subset that is still compilable and post that? — nvoigt
– nvoigt, Commented Feb 7, 2014 at 10:35
You are sending it as const reference, so you cannot change the string inside the function Method() , It is being changed somewhere else. Can you post a sample working code?(SSCCE) — vathsa
– vathsa, Commented Feb 7, 2014 at 10:37
It is strange... you are altering a const reference! Post the implementation of TheClass::Method(const std::string& STR). It is probably a debug configuration which is showing a wrong value. — wesley.mesquita
– wesley.mesquita, Commented Feb 7, 2014 at 10:39
Sounds like memory corruption, run the program through a memory checker (i.e. valgrind on linux). — smani
– smani, Commented Feb 7, 2014 at 11:17

Hans Passant · Accepted Answer · 2014-02-07 11:42:08Z

This quacks loudly like a module boundary problem, calling code in another DLL that was built with an incompatible version of std::string or incompatible compiler settings. Like _HAS_ITERATOR_DEBUGGING.

The only fix for it is recompiling everything with the exact same compiler version, C++ library and build settings.

Exposing C++ objects across module boundaries is a perilous adventure. Especially the ones in the std namespace and especially as of late with C++11 bringing big changes to the standard library implementation. Truly trouble-free DLL interfaces requires pretty draconian measures, the kind that look a lot like COM.

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