Question

I’m trying to write to a file and i get a segmentation fault when i delete the allocated memory. I don’t understant what is the problem, please help:

void writeToLog(string msg) {

    int len = msg.size()+1;
        char *text = new char(len);
    strcpy(text,msg.c_str());
    char* p = text;
    for(int i=0; i<len; i++){
        fputc(*p, _log) ;
        p++;
    }
    delete[] text;   //THIS IS WHERE IT CRASHES
}

I also tried without the [ ] but then i get
*** glibc detected *** ./s: free(): invalid next size (fast): 0x09ef7308 ***

So what is the problem?

Thanks!

Answer 1

Well, delete[] doesn’t balance new char(N), it balances new char[N]. The former creates a pointer to a single char and gives it the value N; the latter creates a pointer to an array of char with length N, and leaves the values indefined.

Of course, to write a std::string to a FILE *, why not just do:

fwrite(msg.c_str(), sizeof(char), msg.size() + 1, _log);

Note that preserves the trailing null character; so does your original code.