How to concatenate path and varying file names - C++

Question

This is my code:

double loglikelihood = 0; 
double loglikelihood1 = 0;
double THRESHOLD = 5;
double c = THRESHOLD + 1; 

std::ofstream llh_file;
std::ofstream myfile;   
const char *path= "path_of_file_to_be_saved";
myfile = ( string(path) + flags.inference_result_file_.c_str() ); 

for (int iter = 0; c > THRESHOLD; ++iter) {     
    std::cout << "Iteration " << iter << " ...\n";  
    loglikelihood = 0; 

    llh_file.open(myfile.c_str() );
    loglikelihood += sampler.LogLikelihood(&document);
    llh_file << "THE LOGLIKELIHOOD FOR ITER " << iter << " " << "IS: " << loglikelihood << "\n";                  
    llh_file.close();

I am a newbie to C++. I have a folder containing different file names. I want to do some process in the for loop and save the results in the folder with the exact file names as the input files. How do I do it? Please help!

Read more about Programming using C++; use C++11 at least; learn about std::string, see here — Basile Starynkevitch
– Basile Starynkevitch, Commented Feb 2, 2016 at 9:08
Folders are OS specific; POSIX and Linux have directories, not folders. You could have a C++ implementation without any kind of folder (and even without directories). On POSIX, consider readdir(3) etc... & nftw(3) — Basile Starynkevitch
– Basile Starynkevitch, Commented Feb 2, 2016 at 9:10
See this. Maybe I am nitpicking, but if you googled on "read directory" you'll immediately find what I mention. Your question should mention what operating system you are interested in. Or consider POCO or Qt. BTW C++11 does not know about folders or directories. — Basile Starynkevitch
– Basile Starynkevitch, Commented Feb 2, 2016 at 9:15

Gabrielle de Grimouard · Accepted Answer · 2016-02-02 09:27:46Z

5

To concatenate strings. Use std::string instead of char*. like:

#include <string>
#include <iostream>
#include <fstream>
int main() {
    std::string path = "path";
    std::string file = "file.txt";
    std::string myfile = path + "/" + "file.txt";
    std::string fname = "test.txt";
    std::ofstream f(fname);
    f << myfile;
}

this will write "path/file.txt" in the file named test.txt.

edited Feb 2, 2016 at 9:27

answered Feb 2, 2016 at 9:11

Gabrielle de Grimouard

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3 Comments

Sanathana Over a year ago

this is exactly what I want. But, I want to save it in a file. This is printing the output. How to save it in a file as the input file name? The input file is in flags.inference_result_file_.c_str(). I am trying to save it in a file.

Gabrielle de Grimouard Over a year ago

edited to write a string in a file. But you will have to adapt it to your code. I won't do all your job :)

Sanathana Over a year ago

hehe.. I figured it out ;) Thanks for the help :)

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