Write vector values into multiple files at once in C++ - c++

Question

I have the data in my vector. I am trying to write each vector value, say vector_name[0] into "examplezero.h" , vector_name[1] into "exampleone.h" and so on. The below code shows how I have created the files.
int co = 80;
string name ="example";
std::ofstream output_file[80];
for (int i = 0; i < co; i++)
{
output_file[i].open(name + std::to_string(i) + ".h");
output_file[i].close();
}
I am trying to iterate over my vector and trying to write to my files.
std::vector<string> rowname; //This has all the values
for (auto i = rowname.begin(); i != rowname.end(); ++i)
{
std::ostream_iterator<std::string> \
output_iterator(output_file[80], "\n");
std::copy(rowname.begin(), rowname.end(), output_iterator);
}
When I am trying to write to the files it is crashing. Can you let me know what's wrong? I know the basics of C++ and trying to learn the advanced concepts.
Thanks

Answer 1

Your program is likely crashing because you wrote this code:
std::ostream_iterator<std::string> \
output_iterator(output_file[80], "\n");
...and output_file[80] is one element past the end of the array. You declared it as:
std::ofstream output_file[80];
The first element of that array is output_file[0] and the last element of that array is output_file[79].
There are more things wrong
As #walnut pointed out, if your code is really as you posted it, then it appears to close each file immediately after opening it, without writing anything to the file.
for (int i = 0; i < co; i++)
{
output_file[i].open(name + std::to_string(i) + ".h");
output_file[i].close(); // Leaving so soon?
}
Writing to an ofstream that has been closed does not crash the program, but sets an error condition on the ofstream (badbit). So this will appear to be a silent failure to you.
To fix
To fix your problem you'll have to write to your file after you open it, but before you close it.
You'll also have to decide exactly which output_file you actually want to write to and provide the correct array index. It's not obviously clear from your sample code what your intent was. You'll have to decide which file(s) (of the 80 that you opened) you want to write each element of your rowname vector into.
The std::copy as you have written it will write all strings in the rowname vector to the same stream. If your intent was to write each element to its own file, then you'll have to set it up substantially differently.
Something more along the lines of:
#include <fstream>
#include <vector>
#include <string>
int main() {
std::vector<std::string> rowname = { "alpha", "bravo", "charlie" }; // example data
std::string name = "example"; // base filename
for (size_t i = 0; i < rowname.size(); ++i) {
std::ofstream output_file;
std::string filename = name + std::to_string(i) + ".h"; // e.g.: "example0.h"
output_file.open(filename);
output_file << rowname[i]; // write the string to the file
output_file.close(); // if you want
}
}
This writes the text alpha into example0.h, bravo into example1.h, and charlie into example2.h.