C++ How to pass command line argument to read txt file

Question

What I've been trying to do is...

1) to read txt files by command line argument,

2) to use strings in the txt files as arguments for the main method (or whatever method you need to invoke).

For example, there are two txt files, one of which is named character.txt and the other match.txt.

The contents of the files would be like this.

character.txt

//This comprises of six rows. Each of the rows has two string values
Goku Saiyan
Gohan Half_Saiyan
Kuririn Human
Piccolo Namekian
Frieza villain
Cell villain

match.txt

//This comprises of three rows, each of them is one string value
Goku Piccolo
Gohan Cell
Kuririn Frieza

If I use those strings without using command line, I'd declare the strings in character.txt like this.

typedef string name; //e.g. Goku
typedef string type; //e.g. Saiyan, Human, etc

Now I'm looking for how to read and send string values from txt files like the ones above, and to use them for functions inside the main method, ideally like this way.

int main(int argc,  char *argv)
{
    for (int i = 1; i < argc; i++) {

        String name = *argv[i]; //e.g. Goku
        String type = *argv[i]; //e.g. Saiyan, Human, etc
        String match = * argv[i]; //Goku Piccolo
        //I don't think any of the statements above would be correct.
        //I'm just searching for how to use string values of txt files in such a way

        cout << i << " " << endl; //I'd like to show names, types or matchs inside the double quotation mark. 
    }
}

Ideally, I'd like to invoke this method in this way.

According to this web site. , at least I understand it is possible to use command line arguments with C++, but I cannot find any more information. I'd appreciate if you'd give any advice on it.

PS. I'm using Windows and Code Blocks.

Answer 1

to see how to use command line arguments look at this.

http://www.cplusplus.com/articles/DEN36Up4/

you cannot use the contents of the file which you have passed to your app through command line arguments. only the name of the file is passed to the app.

you should open the file using that name and read its contents. take a look at this:

http://www.cplusplus.com/doc/tutorial/files/

Answer 2

Asuming you just want to read contents of the files and process it, you can start with this code (Without any errors checks tho). It simply gets filenames from command line and reads file contents into 2 vectors. Then you can just process these vectors as u need.

#include <string>
#include <fstream>
#include <iostream>
#include <vector>

std::vector<std::string> readFileToVector(const std::string& filename)
{
    std::ifstream source;
    source.open(filename);
    std::vector<std::string> lines;
    std::string line;
    while (std::getline(source, line))
    {
        lines.push_back(line);
    }
    return lines;
}

void displayVector(const std::vector<std::string&> v)
{
    for (int i(0); i != v.size(); ++i)
        std::cout << "\n" << v[i];
}

int main(int argc,  char **argv)
{
    std::string charactersFilename(argv[1]);
    std::string matchesFilename(argv[2]);
    std::vector<std::string> characters = readFileToVector(charactersFilename);
    std::vector<std::string> matches = readFileToVector(matchesFilename);

    displayVector(characters);
    displayVector(matches);
}

Answer 3

You define main prototype incorrectly. You also need std::ifstream to read files.

If you expect exactly two arguments, you may check argc and extract arguments directly:

int main(int argc, char* argv[]) {
    if(argc != 3) {
        std::cerr << "Usage: " << argv[0] 
                << " name.txt match.txt" << std::endl;
        return 1;
    }

    std::ifstream name_file(argv[1]);
    std::ifstream match_file(argv[2]);

    // ...

    return 0;
}

If you expect unspecified number of files, than you need a loop and an array to save them, ie vector :

int main(int argc, char* argv[]) {
    std::vector<std::ifstream> files;

    for(int i = 1; i < argc; ++i) 
        files.emplace_back(argv[i]);

    // ...

    return 0;
}

And do not forget to check if files are openable.

Answer 4

First the main function prototype should be

    int main(int argc, char **argv)

OR

    int main(int argc, char *argv[])

Second after retrieving files names in the main function you should open each file and retrieve its contents

Third Sample code

    int main(int argc, char* argv[])
    {
        for(int i=1; i <= argc; i++) // i=1, assuming files arguments are right after the executable
           {
               string fn = argv[i]; //filename
               cout << fn; 
               fstream f;
               f.open(fn);
               //your logic here
               f.close();
           }
     return 0;
     }

Answer 5

#include<stdio.h>
#include<stdlib.h>
int main(int argc, char *argv[])
{
    
    FILE *fp = fopen( argv[1], "r");
    char line[50];
   
     
    if (fp == NULL)
    {
        printf("File opening Unsuccessful\n");
        exit(1);
    }
    while (fgets(line , 30 , fp) != NULL)
    {
   
        printf("%s",line);
        
    }
   fclose(fp) ;
   return 0;

 }