How to append text to a text file in C++?

Question

How to append text to a text file in C++? And create a new text file if it does not already exist and append text to it if it does exist.

http://cplusplus.com/reference/iostream/ofstream/open/ – bobobobo Mar 06 '10 at 17:40 — bobobobo, Mar 06 '10 at 17:40

score 323 · Accepted Answer · edited Nov 06 '19 at 21:33

323

You need to specify the append open mode like

#include <fstream>

int main() {  
  std::ofstream outfile;

  outfile.open("test.txt", std::ios_base::app); // append instead of overwrite
  outfile << "Data"; 
  return 0;
}

edited Nov 06 '19 at 21:33

NathanOliver

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answered Mar 06 '10 at 17:27

Bertrand Marron

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No need to close the file manually, as it does so upon destruction. See http://stackoverflow.com/questions/748014/. Also, is not being used in the example. – swalog Sep 12 '13 at 15:47
7

You can use ios::app in place of ios_base::app – Trevor Hickey Jul 09 '15 at 17:50
5

Can use `std::ofstream::out | std::ofstream::app` instead of `std::ios_base::app`? http://www.cplusplus.com/reference/fstream/ofstream/open/ – Volomike Feb 25 '16 at 22:12
6

You can also do more in the constructor if you want to cut down on code: std::ofstream outfile("test.txt", std::ios_base::app); – marsh Nov 03 '16 at 17:17
You don't need to specify the `out` flag explicitly when using `std::ofstream`, it always uses the `out` flag implicitly for you. Same with the `in` flag for `std::ifstream`. You would have to specify the `in` and `out` flags explicitly if you were using `std::fstream` instead. – Remy Lebeau Nov 06 '19 at 22:31
Also instead of `std::ios_base::app` you can use shorter `std::ios::app`. – Arty Nov 05 '20 at 09:26

score 13 · Answer 2 · answered Sep 13 '16 at 04:22

I use this code. It makes sure that file gets created if it doesn't exist and also adds bit of error checks.

static void appendLineToFile(string filepath, string line)
{
    std::ofstream file;
    //can't enable exception now because of gcc bug that raises ios_base::failure with useless message
    //file.exceptions(file.exceptions() | std::ios::failbit);
    file.open(filepath, std::ios::out | std::ios::app);
    if (file.fail())
        throw std::ios_base::failure(std::strerror(errno));

    //make sure write fails with exception if something is wrong
    file.exceptions(file.exceptions() | std::ios::failbit | std::ifstream::badbit);

    file << line << std::endl;
}

Osaid · Answer 3 · 2014-04-24T15:09:09.973

11

 #include <fstream>
 #include <iostream>

 FILE * pFileTXT;
 int counter

int main()
{
 pFileTXT = fopen ("aTextFile.txt","a");// use "a" for append, "w" to overwrite, previous content will be deleted

 for(counter=0;counter<9;counter++)
 fprintf (pFileTXT, "%c", characterarray[counter] );// character array to file

 fprintf(pFileTXT,"\n");// newline

 for(counter=0;counter<9;counter++)
 fprintf (pFileTXT, "%d", digitarray[counter] );    // numerical to file

 fprintf(pFileTXT,"A Sentence");                   // String to file

 fprintf (pFileXML,"%.2x",character);              // Printing hex value, 0x31 if character= 1

 fclose (pFileTXT); // must close after opening

 return 0;

}

edited Apr 24 '14 at 15:09

answered Nov 01 '12 at 16:27

Osaid

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This is C way, not C++. – Dženan Jul 14 '14 at 11:07
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@Dženan. C being a subset of C++ does not invalidate this approach. – Osaid Sep 12 '14 at 09:13
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@Osaid C is not a subset of C++. Compilers compile its code for backward compatibility. Many C-valid things are not C++-valid things, e.g. VLA. – stryku Feb 18 '18 at 14:00
but if we want to append text in the middle of file? with C style? using FILE *?? "a+" or "a" with fseek() and ftell() didn't worked for me – vincent thorpe Mar 25 '19 at 19:49

score 2 · Answer 4 · edited May 04 '18 at 01:36

2

I got my code for the answer from a book called "C++ Programming In Easy Steps". The could below should work.

#include <fstream>
#include <string>
#include <iostream>

using namespace std;

int main()
{
    ofstream writer("filename.file-extension" , ios::app);

    if (!writer)
    {
        cout << "Error Opening File" << endl;
        return -1;
    }

    string info = "insert text here";
    writer.append(info);

    writer << info << endl;
    writer.close;
    return 0;   
}

I hope this helps you.

edited May 04 '18 at 01:36

Kevin Anderson

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answered Apr 03 '18 at 13:05

Tom

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don't you need writer.close(); with parentheses? – markgalassi Sep 13 '20 at 21:28

score 2 · Answer 5 · edited Jun 25 '18 at 10:32

2

You could use an fstream and open it with the std::ios::app flag. Have a look at the code below and it should clear your head.

...
fstream f("filename.ext", f.out | f.app);
f << "any";
f << "text";
f << "written";
f << "wll";
f << "be append";
...

You can find more information about the open modes here and about fstreams here.

edited Jun 25 '18 at 10:32

Georgy

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answered May 04 '18 at 01:30

ranu

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score 2 · Answer 6 · answered Jan 28 '19 at 08:45

2

You could also do it like this

#include <fstream>

int main(){   
std::ofstream ost {outputfile, std::ios_base::app};

ost.open(outputfile);
ost << "something you want to add to your outputfile";
ost.close();
return 0;
}

answered Jan 28 '19 at 08:45

vveil

123
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Passing the filename to the `ofstream` constructor opens the file immediately, so calling `open()` afterwards is redundant. – Remy Lebeau Nov 06 '19 at 22:32
also `ost.close();` is redundant as it's called in the `std::ofstream` destructor. – Mohamed Kandeel Apr 06 '21 at 10:26

How to append text to a text file in C++?

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