Go4Expert - How to print a String class string to a txt file

Go4Expert (http://www.go4expert.com/)

- C++ (http://www.go4expert.com/forumdisplay.php?f=100)

- - How to print a String class string to a txt file (http://www.go4expert.com/showthread.php?t=8570)

How to print a String class string to a txt file

Hi, I had a problem in printing a String class string to a file where I had declared:

string str1[10], str2[10];

And in str1[6] and str2[6] has the values which I wanna store the values by writing them to a txt file using the format:

// write to apsignal.txt
newfile= fopen("apsignal.txt","w");
if (newfile==NULL)
{
cout<<"Error opening apsignal.txt";
fclose(newfile);
return -1;
}

//Print to file with the signal strengths and corresponding clientIDs.
fprintf(newfile,"1" " %s" " %s", &str1[6], &str2[6] );
fclose(newfile);

however, it seems like it cannot print out the values in the txt file as it is a string class? So I was wondering if anyone can give me other alternatives to write the values into this text file?

Thanks! I had attached the relevant files and pls take a look at the apsignal.txt and you will know what I mean. Thanks for any help!

Re: How to print a String class string to a txt file

Well if you're going to continue to use the C API in a C++ program (I don't recommend it), then it would be

fprintf(newfile,"1" " %s" " %s", str1[6].c_str(), str2[6].c_str() );

Re: How to print a String class string to a txt file

Sorry for the late reply...well...I've followed the way u coded by changing the fprintf to fprintf (newfile, "Test: %s %s\n", str1.c_str(), str2.c_str()); but it doesn't seem to work. Is there anything I need to import or I've left it out?

Re: How to print a String class string to a txt file

I Download your attached file but I found nothing in them except some garbage text.
Anyway
Check This code

Code:

#include <iostream>

#include <cstdlib>

#include <cctype>

#include <fstream>

#include <cstdio>

using namespace std;



int main()

{

    string str[4]={"abc","def","ghi","jkl"};

/* c++ code

    fstream f;

    f.open("abc.txt",ios::out);

    if(!f)

    {

        cout<<"Cannot Open File";

        return 0;

    }

    f<<str[2];

    f.close();

    f.open("abc.txt",ios::in);

    if(!f)

    {

        cout<<"Cannot Open File";

        return 0;

    }

    f>>str[1];

    cout<<str[1];

    f.close();

*/

// C Code

    FILE *fp;

    fp = fopen("abc.txt","w");

    if(fp==NULL)

    {

        cout<<"Cannot Open File";

        return 0;

    }

    fprintf(fp,"%s",str[2].c_str());

    fclose(fp);

        return 0;

}

For me this code works fine. I think you are using C code in c++. Maybe you are getting this warning if you are using GCC compiler

Quote:

warning: cannot pass objects of non-POD type `struct std::string' through `...'; call will abort at runtime

This error occurs because
The %s argument requires a c-styled string, but you've passed it an actual std::string object.
[/quote]
Check my above code in c++ code is working fine. Even if you are using %s then use c_str() function to convert it into const char *.

Quote:

//Print to file with the signal strengths and corresponding clientIDs.
fprintf(newfile,"1" " %s" " %s", &str1[6], &str2[6] );
fclose(newfile);

however, it seems like it cannot print out the values in the txt file as it is a string class?

I am not that much strong in C but amazed why you are using & in fprintf() function.

You can more read about POD in this link
http://www.fnal.gov/docs/working-gro...x/doc/POD.html
http://www.digitalfanatics.org/index...CompilerErrors

Regards