I want to concatenate a fileName including path and file names. Then I can open and write it. But I failed to do so. 

```
char * pPath;
pPath = getenv ("MyAPP");
if (pPath!=NULL)
//printf ("The current path is: %s",pPath); // pPath = D:/temp

string str = "test.txt";
char *buf = new char[strlen(str)];
strcpy(buf,str);

fullName = ??  // how can I get D:/temp/test.txt 

ofstream outfile;
outfile.open(fullName);
outfile << "hello world" << std::endl;

outfile.close();

```