CODEWITHSUNDEEP
c++file-iocommand-line-arguments
JuanKman94
JuanKman94

Reputation: 112

C++ Read from text file

everybody. I'm having a rough time trying to code this thing, I hope you can give me some advice. I'm trying to retrieve some parameters from a text file and then append them to a variable char array and then execute that char array with a pipe, the command is a bash command.

My problem is how to access the file to retrieve the parameters, I've tried with buffers and string but conversions haven't really helped, here's the basic idea of my code.

Working code if I write the command directly to the code:

#include <string.h>
#include <cstdlib>
#include <cstdio>

char *out[10], line[256], command[] = {"mycommand parameter1 parameter2 ..."};

FILE *fpipe;

fpipe = (FILE*)popen(command,"r")
fgets(line, sizeof line, fpipe)

out[0] = strtok (line, "=");   // <--- I'm tokenizing the output.

My approach to read from file:

std::ifstream file("/path/to/file", std::ifstream::in);
//std::filebuf * buffer = file.rdbuf();
char * line = new char[];

//buffer->sgetn (line, lenght);

getline(file, line)

The commented line are things I've tried, there were others but I didn't comment them.

I'm considering port it to C later, but first I want to get it going. And I haven't really implemented the append code since I can't read the file yet. Hope you can give me some tips, thanks!

Upvotes: 2

Views: 436

Answers (3)

RealityPC
RealityPC

Reputation: 137

The std::getline() takes istream and string as arguments.

istream& getline (istream& is, string& str);

Here is the documentation: http://www.cplusplus.com/reference/string/string/getline/

Upvotes: 1

Ice
Ice

Reputation: 31

I would advice to do something like :

#include <string>
#include <fstream>

std::istream file("/path/to/file"); //ifstream is only infile

std::string astringpar;
float afloatingpar;
//in this example there is a string and a float in the file
//separated by space, tab or newline
//you can continue/replace with int or other in fonction of the content

while (file >> astringpar >> afloatpar)
{
//here do what you want with the pars
}

ciao Ice

Upvotes: 0

David G
David G

Reputation: 96790

You're on the right track, you just need to use a std::string which is what getline receieves:

std::string line;
std::getline(file, line);

That reads the first line. But if you needed to read the entire contents of the file into line just do:

std::string line;
std::istreambuf_iterator<char> beg = file.rdbuf();
std::istreambuf_iterator<char> end;

line.assign(beg, end);

Upvotes: 2

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