CODEWITHSUNDEEP
c++visual-c++
jerle78
jerle78

Reputation: 157

can't get argv to pass to string

I'm new to C++ programming (haven't done it in 10+ since college.) and I'm trying to write a very basic program to grab a file name that has been passed as an argument. I'm just not getting how to get the file name. I'm using VS2012 Exp for Desktop.

Below is my code.

#include "stdafx.h"
#include <fstream>
#include <iostream>
#include <xstring>
#include <string>

//using namespace openutils;
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
    wcout << "customconsole app has "<< argc <<" arguments passed.  second one is:  " << argv[1];
    ofstream me_attach_file;
    wstring newfilename = argv[1] && ".newext";
    me_attach_file.open (".mailexpress");
    me_attach_file << "Writing this to a file.\n";
    me_attach_file.close();
return 0;
}

Upvotes: 1

Views: 1447

Answers (3)

Jamin Grey
Jamin Grey

Reputation: 10495

&& doesn't add two strings together. The + operator does.

Also, C++ decides which of the many operator + functions to use by the type of the left-hand argument. You have two different types here, a _TCHAR string, a string literal ("this is a string literal") which is type char*, and you want to put it into a wstring.

First, a _TCHAR and char* aren't the same type, so it should be L".newext".

Second, you can't add two char*s, because that is adding two pointers, and pointer arithmatic does something different than what you want. So the first argument needs to be coverted to a wstring before you start adding things together.

Either:

wstring myStr = argv[1];
myStr += L".newext"

Or:

wstring myStr = wstring(argv[1]) + L".newext" + L"Additional stuff"

Upvotes: 3

WoJo
WoJo

Reputation: 370

in the line

me_attach_file.open (".mailexpress");

you should pass the filename to the object.

me_attach_file.open (newfilename);

in your version, ofstream will open a file named ".mailexpress" without prefix (which is hidden on unix systems).

Upvotes: 0

Ben Voigt
Ben Voigt

Reputation: 283941

Replace this

wstring newfilename = argv[1] && ".newext";

with 

wstring newfilename = argv[1];
newfilename += L".newext";

Some languages use & for string concatenation. C++ does not. In fact, there is NO operator that concatenates string literals and character pointers: + as string concatenation is defined by string objects and works only with them.

In addition, string literals have to be prefixed with L to use wide characters and be compatible with wstring.

Upvotes: 3

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