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c++ file reading

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Started by BaneTrapper August 19, 2012 03:17 PM

15 comments, last by Servant of the Lord 11 years, 8 months ago

BaneTrapper

1,535

Author

August 19, 2012 03:17 PM

Hello.
I was using to read data from my files like this



/*text.txt*/

3

./Files/Maps/Map1.txt

./Files/Maps/Map2.txt

./Files/Maps/Map3.txt



FILE* tempFile = fopen("text.txt", "r");

if(tempFile == NULL)

{

    fclose(tempFile);

}

fscanf(tempFile, "%d", &MyInt);

for(int x = 0; x < MyInt; x++)

{

    char tempChar[60];

    fscanf(tempFile, "%s\n", tempChar);

    MyVector.push_back(tempChar);

}

But its really bugging me that i am limited to "char" cause the fscanf "%s" cant store to string.

What libraries can i use to read data from .txt files to string directly , and hopefully are simple to use

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SiCrane

11,840

August 19, 2012 03:31 PM

Well you could use the iostream library.



  std::ifstream file("text.txt");

  std::vector<std::string> lines;

  while (file) {

    std::string line;

    std::getline(file, line);

    lines.push_back(line);

  }

Cornstalks

7,033

August 19, 2012 03:41 PM

Note that if you use the method SiCrane suggested (which I would if I were you), you need to include [font=courier new,courier,monospace]<fstream>[/font] for [font=courier new,courier,monospace]std::ifstream[/font], and [font=courier new,courier,monospace]<string>[/font] for [font=courier new,courier,monospace]std::string[/font] and [font=courier new,courier,monospace]std::getline()[/font].

The way you're currently doing it is the C way. SiCrane's way is the C++ way.

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Serapth

6,672

August 19, 2012 04:03 PM

Too slow, I was about to propose:



#include <iostream>

#include <string>

#include <vector>

#include <fstream>

#include <algorithm>

using namespace std;

int main(int argc, char** argv)

{

ifstream stream;

stream.open("level.txt");

int numFiles;

stream >> numFiles;

cout << numFiles;

vector<string> results;

while(stream)

{

  string str;

  getline(stream,str);

  if(str != "") // Handle empty newlines

   results.push_back(str);

}

std::for_each(results.begin(),results.end(), [](string value) { cout << value << endl; });

return 0;

}

Wow, the C++ formatter is seriously broken...

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Tudor Nita

122

August 20, 2012 11:38 AM

I wouldn't use iostream. Something like this works for me. Imagine an input file like:

# a comment
a 3.5 3.5 yay_some_text
a 3.2 4.5 yay_some_more_text

[source lang="java"]FILE *pFile = fopen(filePath, "r"); // the file to load

char buffer[512]; // character buffer
char temp;
// read each line into the buffer
while (fgets(buffer, sizeof(buffer), pFile))
{
// switch based on leading type
switch (buffer[0])
{
case '#': // do nothing, it's a comment

break;
case 'a':
// set ambient color ?
sscanf(buffer, "%c %f %f %s", &temp, &someFloat, &someOtherFloat, &aString);
break;
}

}[/source]

Bregma

9,461

August 20, 2012 11:42 AM

I wouldn't use iostream.

Can you expand on that?

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Professional Free Software Developer

Tudor Nita

122

August 20, 2012 11:55 AM

Just personal preference I guess. It's a bit verbose for my liking and enforces type safety at compile time. This nags at me a bit too: http://stackoverflow...answer-5165293

Seeing how I'm really used to the fgets way, this is all, of course, highly subjective. Still, it's a valid alternative.

BitMaster

8,652

August 20, 2012 12:09 PM

Type safety is a good thing. Actually it is a great thing.

And while it's true that the iostream classes can be a bit on the slow side on a lot of implementations, I would not replace them with something handrolled like that. If performance of text file parsing is an issue (in a lot of cases it is not), I would rather use a proper lexer generator. It will usually be just as fast, much easier to maintain and much safer.

SiCrane

11,840

August 20, 2012 12:27 PM

Two additional things: 1) the stdio API becomes just as verbose as iostreams, if not more so, when you actually do error handling. 2) your code doesn't actually address the OPs original complaint: not being able to work with string objects directly.

Hodgman

52,717

August 20, 2012 01:11 PM

<br />This nags at me a bit too: http://stackoverflow...answer-5165293<br />

N.B. If you want to avoid the formatting overhead of fstream, you can shed one layer of abstraction by accessing it's internal filebuf object, though obviously you're now responsible for doing some of the work that the stream used to do for you.

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c++ file reading

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