inserting int variable in file name

Question

Possible Duplicate:
Easiest way to convert int to string in C++

How can I insert int variable while creating .vtk file? I want to create file at every k step. i.e. so there should be series of files, starting from file_no_1.vtk, file_no_2.vtk, ... to file_no_49.vtk .

while(k<50){
  ifstream myfile;

  myfile.open("file_no_.vtk");

  myfile.close();

  k++;
}

Dupe of all of the `How to convert int to string?` questions here. Just so you know, there's a `std::to_string` function in C++11. — chris, Jul 11 '12 at 17:03

Robᵩ · Accepted Answer · 2012-07-11T17:35:19.113

16

In C++11:

while(k<50){
  ifstream myfile("file_no_" + std::to_string(k) + ".vtk");
  // myfile << "data to write\n";
  k++;
}

edited Jul 11 '12 at 17:35

answered Jul 11 '12 at 17:06

Robᵩ

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+1: `std::to_string`? That's neat. – Zeta Jul 11 '12 at 17:08
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@Zeta, I was ecstatic when I saw someone here mention that and `std::stoi`, but depressed when I found out my implementation doesn't have either >.> – chris Jul 11 '12 at 17:09
@chris: I recall it was me who mentioned `std::stoi` and you commented on my post. :-/ – Nawaz Jul 11 '12 at 17:11
@Nawaz, It very well might have been. Thank you if it was, as at least I can recommend it to others :) – chris Jul 11 '12 at 17:12
4

Not the first time I stole I good idea from @Nawaz. – Robᵩ Jul 11 '12 at 17:12

score 4 · Answer 2 · answered Jul 11 '12 at 17:07

4

Use a stringstream (include <sstream>):

while(k < 50){
    std::ostringstream fileNameStream("file_no_");
    fileNameStream << k << ".vtk";

    std::string fileName = fileNameStream.str();

    myfile.open(fileName.c_str());

   // things

    myfile.close();

    k++;
}

answered Jul 11 '12 at 17:07

Zeta

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I want to point out that there was a question recently that used `myfile.open (fileName.str().c_str());`, causing the confusion. Make sure not to do that, and instead make the string variable. – chris Jul 11 '12 at 17:14

score 3 · Answer 3 · answered Jul 11 '12 at 17:03

3

Like this:

char fn [100];
snprintf (fn, sizeof fn, "file_no_%02d.vtk", k);
myfile.open(fn);

Or, if you don't want the leading zero (which your example shows):

snprintf (fn, sizeof fn, "file_no_%d.vtk", k);

answered Jul 11 '12 at 17:03

wallyk

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+1 despite the potentially confusing variable names – Sam I am says Reinstate Monica Jul 11 '12 at 17:04
@SamIam: Is `fn` for filename confusing? – wallyk Jul 11 '12 at 17:05
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`MAGIC_BUFFER_SIZE`? Hideously unsafe `sprintf`? You should be ashamed of yourself for posting this as a C++ answer. – Puppy Jul 11 '12 at 17:05
@wallyk it's certainly harder to recognize than say... `fileName` would be. – Sam I am says Reinstate Monica Jul 11 '12 at 17:06
@DeadMG: Okay, it is fairly well improved. Magic buffer size: hrrmmpph! It is right there to see for excellent maintenance. – wallyk Jul 11 '12 at 17:07
@wallyk: No. The only acceptable buffer size is "The one I computed was necessary". – Puppy Jul 11 '12 at 17:07
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@DeadMG: There is absolutely no chance of a problem occurring by using `snprintf` in this way. – Ed S. Jul 11 '12 at 17:07
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@DeadMG: Simplest thing that can possible work FTW!!!! – Sam I am says Reinstate Monica Jul 11 '12 at 17:08
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@DeadMG: you are adding needless complexity to avoid a problem which is easily detected. In the process, you are contributing to a less maintainable body of code. – wallyk Jul 11 '12 at 17:09
@SamIam: Except it won't work, because tomorrow some intern will edit the string to be longer than 100 characters, and you will bite UB. Rob's answer is the most concise, most maintainable, and guaranteed correctness. – Puppy Jul 11 '12 at 17:09
@SamIam: Point taken. But also see [beauty in brevity](http://stackoverflow.com/a/4351938/198536) – wallyk Jul 11 '12 at 17:10
@wallyk Point taken? I didn't have a point that was contrary to yours – Sam I am says Reinstate Monica Jul 11 '12 at 17:11
@SamIam: I thought your point was that `fileName` is more readable than `fn`. – wallyk Jul 11 '12 at 17:12

inserting int variable in file name

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