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Command line arguments

Posted on 2009-05-20
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Last Modified: 2012-05-07
I'm using MS Visual Studio 2005 and creating a Windows console application.  It seems to me the reading of command line arguments is not working correctly.
In the code below, argv[n] only contains the first character of the command line input.

I get the following output:

C:\myproject>test.exe 123 abc
Argument 0:  t
Argument 1:  1
Argument 2:  a

I expected argv to contain
test.exe
123
abc

What am I doing wrong?

Thanks.
// test.cpp : Defines the entry point for the console application.
//
 
#include "stdafx.h"
#include "stdio.h"
#include "string.h"
 
 
int _tmain(int argc, _TCHAR* argv[])
{
	for ( int i=0; i < argc; i++ ){
 
		printf("Argument %i:  %s\n", i, argv[i]);
	}
	return 0;
}

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Question by:JohnSantaFe
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11 Comments
 
LVL 40

Expert Comment

by:mrjoltcola
ID: 24434434
Probably because you are using a TCHAR type for argv, I don't think that works.

Try:

int _tmain(int argc, char* argv[])
{
        for ( int i=0; i < argc; i++ ){
 
                printf("Argument %i:  %s\n", i, argv[i]);
        }
        return 0;
}

I will look it up, but I think the standard requires argv to be a standard char **
0
 
LVL 40

Accepted Solution

by:
evilrix earned 2000 total points
ID: 24434445
The reason is because the arguments are wide chars so every second byte int he 16 byte TCHAR is a null so it's being cut short.

Try this...

for ( int i=0; i < argc; i++ ){
 
           std::wcout << "Argument " << i << ": " << argv[i];
}

Remember to include iostream for this to work.
0
 
LVL 40

Expert Comment

by:evilrix
ID: 24434472
>> Probably because you are using a TCHAR type for argv, I don't think that works.
Sure it does... Microsoft compiles will allow Wide or Narrow for argv, this is the default of how the compiler creates a project. The problem is if it's wide the 2nd bytes are most likely 0

e.g.

'A' == 0x41
L'A' == 0x4100

But %s is expecting a stream of narrow chars so when it hits the 2nd byte in the wide char it sees a null and terminates
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LVL 40

Expert Comment

by:mrjoltcola
ID: 24434496
You are right, I just looked at some UNICODE projects, and I had never even noticed argv was wide character!

0
 
LVL 9

Expert Comment

by:JohnGaby
ID: 24434537
_wprintf is the wide version of printf.  If you use _tprintf then it will map to the wide version if you are using unicode (which is default for 2005), or to the ansi version if you are not using unicode:

http://msdn.microsoft.com/en-us/library/wc7014hz(VS.80).aspx
0
 

Author Comment

by:JohnSantaFe
ID: 24434554
Well,

Switching to char* didn't work.

Using _TCHAR*  and wcout worked.

But I don't quite get it.  Seems like this would break a million console applications....?
0
 

Author Comment

by:JohnSantaFe
ID: 24434579
Ah, I see, when using _tmain you get the wide version.

When I used the code below it worked as expected.

Thanks.

#include "stdafx.h"
#include "stdio.h"
#include "string.h"
 
 
 
 
 
int main(int argc, char* argv[])  //note changed from _tmain()
{
	for ( int i=0; i < argc; i++ ){
 
		printf("Argument %i:  %s\n", i, argv[i]);
 
	}
	return 0;
}

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0
 
LVL 40

Expert Comment

by:evilrix
ID: 24434594
>> But I don't quite get it.  Seems like this would break a million console applications....?
Wide chars (in Windows) are 2 bytes and narrow are 1. Most of the standard narrow ASCII chars map to wide chars by just setting byte 0 to be the same as the narrow value and byte 1 to 0x00. This is a null char and since C functions user null to signify the end of a string that's why you only see the first char.

When you try and printf L'A' it see 2 chars, 'A' and '\0'
0
 
LVL 40

Expert Comment

by:mrjoltcola
ID: 24434603
>>Ah, I see, when using _tmain you get the wide version.

You and I both, I also did not notice _tmain before responding so I learned something as well.
0
 

Author Closing Comment

by:JohnSantaFe
ID: 31583622
Thanks for the help.
0

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