Saving into a variable file name

Posted on 2014-09-25
Last Modified: 2014-09-28
I need to write to a file name depending on a couple of variables and I'm having a hard time doing it. I got several different errors but couldn't find an answer anywhere in my books or the web on how it could be solved.

I'm using the following code and it works fine, but when I try to use the variables to use in the creation for the file and than it all goes wrong:

Working one
ofstream fout("C:/Users/rodrigo/Desktop/myfile.txt");

int somevar;
int yetanothervar;
somevar = 1;
yetanothervar = 3;
string address;
address = "C:/Users/rodrigo/Desktop/"+somevar+yetanothervar+".txt";
ofstream fout(address);

Any help would be much apreciated.
Question by:Rodric MacOliver
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LVL 16

Expert Comment

ID: 40344992
Add quotations on your address output?
LVL 86

Accepted Solution

jkr earned 250 total points
ID: 40345029
You can't add a string and an integer to form a new string like you can in e.g. C# - in C++ you need a stringstream, e.g.

#include <sstream> // <-- add this one

int somevar;
int yetanothervar;
somevar = 1;
yetanothervar = 3;

stringstream ss;

ss << "C:/Users/rodrigo/Desktop/" << somevar << yetanothervar <<".txt"; // create file name

string address;
address = ss.str();

ofstream fout(address);

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LVL 34

Assisted Solution

sarabande earned 250 total points
ID: 40345495
ofstream fout(address);

Open in new window

that will not compile. use address.c_str() as argument instead.

the usage of string streams could be improved by defining the following macro (you may put it into a common header file).

#define VARFILENAME(s) ((std::ostringstream&)((std::ostringstream())<<s)).str().c_str()

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then you can do

std::ofstream fout(VARFILENAME("C:/Users/rodrigo/Desktop/" << somevar << yetanothervar <<".txt"));

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the macro could be used not only for filenames but for any other purpose where required type is const char *.


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