Getting chars from argv

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The app is Windows 7 Enterprise, MFC, Visual Studio 2008, C++, unicode enabled

The argument needed is a single character. VS is configured to provide command line argument, value is "1", argc has incremented from 1 to 2 after adding the command line argument.

char str_number = __argv[ 1 ];

Compile error cannot convert from char* to char, cool, understood

char str_number = *__argv[ 1 ];

Access violation reading location 0x00000004

char str_number = *__argv[ 1,0];

Access violation reading location 0x00000000

What I have tried:

I have tried the examples shown in block: Describe the problem.

Posted 12-Oct-16 6:24am

bkelly13

Updated 12-Oct-16 10:25am

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Patrice T 12-Oct-16 12:31pm

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3 solutions

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Richard MacCutchan · Answer 1 · 2016-10-12T06:45:00

Solution 2

You first need to check the value of __argc before attempting to refer to any of the __argv elements. Something like:

C++

if (__argc > 1)
    char str_number = *__argv[ 1 ];

Alternatively you can use the CCommandLineInfo Class[^].

Posted 12-Oct-16 6:45am

Richard MacCutchan

CPallini · Answer 2 · 2016-10-12T10:25:00

Solution 3

Both

char str_number = *__argv[1];

and

char str_number = __argv[1][0];

should work.

Please check always __argc value before accessing __argv, as pointed out by Richard.

Posted 12-Oct-16 10:25am

CPallini

nv3 · Answer 3 · 2016-10-12T06:44:00

Solution 1

When your application is unicode enabled you should use __wargv instead of __argv. Try your second example again with that change and you should be in luck.

Posted 12-Oct-16 6:44am

nv3

Comments

Richard MacCutchan 13-Oct-16 3:09am

How will that help when OP is trying to access a char?

nv3 13-Oct-16 3:56am

He is trying to access the first character of the first argument. *__argv[1] should normally do that. But in the case of a unicode application, windows doesn't deliver the argument vector in __argv, but in __wargv instead. That's probably why he got the access violation.