fstream won't create a file [duplicate]

问题:

This question already has an answer here:

• std::fstream doesn't create file 2 answers

I'm simply trying to create a text file if it does not exist and I can't seem to get fstream to do this.

#include <fstream>
using std::fstream;

int main(int argc, char *argv[]) {
    fstream file;
    file.open("test.txt");
    file << "test";
    file.close();
}

Do I need to specify anything in the open() function in order to get it to create the file? I've read that you can't specify ios::in as that will expect an already existing file to be there, but I'm unsure if other parameters need to be specified for a file that does not already exist.

回答1:

You should add fstream::out to open method like this:

file.open("test.txt",fstream::out);

More information about fstream flags, check out this link: http://www.cplusplus.com/reference/fstream/fstream/open/

回答2:

You need to add some arguments. Also, instancing and opening can be put in one line:

fstream file("test.txt", fstream::in | fstream::out | fstream::trunc);

回答3:

This will do:

#include <fstream>
#include <iostream>
using std::fstream;

int main(int argc, char *argv[]) {
    fstream file;
    file.open("test.txt",std::ios::out);
    file << fflush;
    file.close();
}