I'm trying to create an ofstream and then write values from an array into it.
void Graph::toFile(char* filename)
{
ofstream outfile(filename.c_str()+"_new.txt");
for(int i = 0; i < noOfVertices; i++)
outfile << graphPartition[i] << endl;
outfile.close();
}
My main problem is, that I want the output file to be named filename+"new.txt". However, there is something wrong with my approach, because i keep getting an error expression must have class type.
I'm really sorry, if this question is a duplicate, I haven't found an satisfying solution.
Your problem is that filename is not std::string it's a c-string (char*). C-strings are not objects, they don't have methods, they're just a pointer to a zero-terminated array of characters in memory.
filename.c_str()
-^-
The second problem you'd have with this approach, if filename was a std::string, is that adding two C-string pointers doesn't concatenate the strings, it simply does math on the pointers, giving you an address equal to the address returned by filename.c_str() plus the address of "_new.txt"
If you change your code to receive the filename as a std::string
void Graph::toFile(std::string filename)
then you can do the following:
filename += "_new.txt";
As follows:
void Graph::toFile(std::string filename)
{
filename += "_new.txt";
ofstream outfile(filename.c_str());
or
void Graph::toFile(std::string filename)
{
ofstream outfile(filename + "_new.txt");
Demo:
#include <iostream>
#include <string>
void Graph_toFile(std::string filename)
{
filename += "_new.txt";
std::cout << "opening " << filename << "\n";
}
int main() {
Graph_toFile("hello_world");
return 0;
}