assignment of c_str() to a string

Question

I have a problem which i cannot fix on my own.

string filenameRaw;
filenameRaw= argv[1];
function(filenameRaw.c_str(),...);

function(const char* rawDataFile,const char* targetfieldFile,const char* resultFile,const char* filename)
...
this->IOPaths.rawData=rawDataFile;
...

works very fine so far. Now I try to put another string in the variable IOPaths.rawData...

function(const char* rawDataFile,const char* targetfieldFile,const char* resultFile,const char* filename)
...
string filenameRaw;
filenameRaw=reader.Get("paths", "rawData", "UNKNOWN")
...
const char* rawDataFile1=filenameRaw.c_str();
cout << "Compare: " << strcmp(rawDataFile,rawDataFile1) <<endl;
...
this->IOPaths.rawData=rawDataFile1;

this does not work any more. Later in my programm I get errors with the filename. The strcmp definitly gives a 0, so the strings must be equal. Does anyone has an idea what i am doing wrong?

Answer 1

The validity of the output of c_str() is limited to, at most, the lifetime of the object on which c_str() was called.¹

I suspect that this->IOPaths.rawData is pointing to deallocated memory once filenameRaw is out of scope.

An adequate remedy would be to pass the std::string around rather than [const] char*. A good stl implementation would use copy on write semantics for the string class so perhaps you wouldn't be repeatedly copying string data.

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¹In certain instances (such as if the object is modified), it could be less.