如果文件存在,请使用它,如果不存在,则创建它

Question

fstream datoteka;
datoteka.open("Informacije.txt",  fstream::in | fstream::out | fstream::app);

if(!datoteka.is_open()){              
    ifstream datoteka("Informacije.txt")
    datoteka.open("my_file.txt", fstream::in | fstream::out | fstream::app);
}/*I'm writing IN the file outside of that if statement.

所以它应该做的是创建一个文件,如果它之前没有创建,如果它被创建写入该文件.

你好,所以我想从我的程序中检查文件是否已经存在,如果它已经存在则打开程序并且我可以在其中写入,如果文件未打开(之前没有创建)程序创建它.所以问题是当我创建一个.csv文件,并完成写入,我想检查写入是否真的存在,该文件无法打开.在.txt文件中,一切都是空白的.

Answer 1

如果文件名不存在，则创建该文件。否则，fstream::app，如果文件filename已经存在，则将数据附加到文件而不是覆盖它。

int writeOnfile (char* filetext) {
       ofstream myfile;
       myfile.open ("checkSellExit_file_output.csv", fstream::app);
       myfile << filetext;
       myfile.close();
       return 0;
    }

Answer 2

datoteka.open(filename, std::fstream::in | std::fstream::out | std::fstream::app); 工作良好.

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

int main(void)
{

     char filename[ ] = "Informacije.txt";
     fstream appendFileToWorkWith;

     appendFileToWorkWith.open(filename, std::fstream::in | std::fstream::out | std::fstream::app);


      // If file does not exist, Create new file
      if (!appendFileToWorkWith ) 
      {
        cout << "Cannot open file, file does not exist. Creating new file..";

        appendFileToWorkWith.open(filename,  fstream::in | fstream::out | fstream::trunc);
        appendFileToWorkWith <<"\n";
        appendFileToWorkWith.close();

       } 
      else   
      {    // use existing file
         cout<<"success "<<filename <<" found. \n";
         cout<<"\nAppending writing and working with existing file"<<"\n---\n";

         appendFileToWorkWith << "Appending writing and working with existing file"<<"\n---\n";
         appendFileToWorkWith.close();
         cout<<"\n";

    }




   return 0;
}