WriteFile() Truncating String - c++

Question

std::cout << buffer << std::endl;
if (lastTitle != buffer) {
//write new title;
WriteFile(file, "\n\nWindow: ", sizeof("\n\nWindow: "), NULL, NULL);
WriteFile(file, buffer.c_str(), sizeof(buffer), NULL, NULL);
WriteFile(file, "\n", sizeof("\n"), NULL, NULL);
std::cout << GetLastError(); //this is showing 0, which means no error
Cout is outputting:
C:\Users\riseo\Desktop\C++\my_proj\Debug\my_proj.exe
The file that is being written to is showing:
Window: C:\Users\riseo\Desktop\C++\m
I'm not quite sure why this is being truncated, it should be the same as what cout is printing. Im sorry this post doesn't show much research, but I've been getting burned by various string-format related gotchas all day and I have no clue what is happening here. All I can think of is maybe something with c_str() is going wrong.

Answer 1

You are seriously misusing sizeof(). WriteFile() operates on bytes, but you are passing it character data. String literals contain a null terminator that sizeof() would include, which you don't want in this case. And std::string() contains a pointer to the character data, so sizeof(std::string) does not account for the true character length.
You need to do this instead:
//write new title;
WriteFile(file, "\n\nWindow: ", strlen("\n\nWindow: "), NULL, NULL);
WriteFile(file, buffer.c_str(), buffer.length(), NULL, NULL);
WriteFile(file, "\n", strlen("\n"), NULL, NULL);
A wrapper function would be better:
bool WriteStringToFile(HANDLE hFile, const std::string &str)
{
return WriteFile(hFile, str.c_str(), str.length(), NULL, NULL);
}
...
//write new title;
WriteStringToFile(file, "\n\nWindow: ");
WriteStringToFile(file, buffer);
WriteStringToFile(file, "\n");
A std::ofstream would be even better:
std::ofstream ofs("myfile.txt", std::ios_base::binary);
...
ofs << "\n\nWindow: " << buffer << "\n";