parsing input and output filename as argument from command line

Question

I am new with c++ and in a project i need to use command line argument. I read about command line arguments i.e including

 int main(int argc, char** argv)
{
}

but i have a problem declaring my filename in the source file.

i declared my input and output filename in the source file(file_process.cpp) as

const char iFilename[] ;
const char oFilename[] ;

defined the function(which uses the input file - iFilename and process the output in the oFilename) as

void file_process::process(iFilename[], oFilename[])
{
body...
}

and in the main method as :

int main(int argc, char** argv) {

    iFilename[] = argv[1];
    oFilename[] = argv[2];
    file_process::process(iFilename[], oFilename[]);

}

earlier i hardcoded the filename to test my program without arguments in the main method and declaring the variable in the source file(file_process.cpp)as:

const char iFilename[] = "input_file.pdf";
const char oFilename[]  = "output_file.txt";

and its working fine but when I am trying to take the arguments from the command line as stated above and I am not able to compile it.

Is it the right way of doing it in c++ ? I work with c# and there simply declaring in the source file like:

string iFilename = args[0];
string oFilename = args[1];

works. I

In C++ you would do nearly the same as in C#, that is: std::string iFilename = argv[1], and then pass the variable as a C++-string to the function or as a C-string using std::string::c_str(). — Jonas
– Jonas, Commented Nov 23, 2016 at 9:57
file_process::process will need a type of parameter, not just a name. Don't forget arg[0] is the exe name. Don't forget const where needed. Or use a std::string — doctorlove
– doctorlove, Commented Nov 23, 2016 at 10:05

Jonas · Accepted Answer · 2016-11-23 10:08:10Z

1

Here is one way to do it:

int main(int argc, char** argv)
{
    assert(argc >= 3);
    const std::string iFilename = argv[1];
    const std::string oFilename = argv[2];
    file_process::process(iFilename, oFilename);
}

And you file_process::process could be:

void file_process::process(const std::string& iFilename, const std::string& oFilename)
{
    body...
}

edited Nov 23, 2016 at 10:08

answered Nov 23, 2016 at 10:01

Jonas

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7 Comments

Saurabh Over a year ago

I did as you said But when I am editing my file_process::process as void file_process::process(const std::char& iFilename[], const std::string& oFilename[]); the compiler shows an error in the above line as " error: expected ‘)’ " , though I can't see any need for this closing paranthesis. Another error in the above line is "expected initializer" I initialized the iFilename and oFilename as global const as: const char iFilename[100]; const char oFilename[100];

Jonas Over a year ago

Either go for C-strings or C++-strings you should not mixed, that is just weird. And it is not std::string[] that is an array of std::string...

Saurabh Over a year ago

Thank you for pointing that out it was a typo. I fixed the code now, your second point regarding the array of std::string was helpful indeed. Now I am having the problem at runtime stating "int main(int, char**): Assertion 'argc>=3' failed."

Jonas Over a year ago

The assert is there to ensure you remember to actually provide command-line arguments, if you don't it will assert.

Saurabh Over a year ago

I have another problem in the project now. I am using netbeans and I didn't add arguments in the project properties. Now the project is compiling but at the run time it states /bin/sh: 1: Syntax error: Unterminated quoted string I googled but couldn't find a concrete answer. Any idea what is the problem ?

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