How come argv can be incremented?

This is a discussion on How come argv can be incremented? within the C++ Programming forums, part of the General Programming Boards category; Hi.. we all very much know the base address of an array cannot be incremented ... i mean if i ...

  1. #1
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    How come argv can be incremented?

    Hi..


    we all very much know the base address of an array cannot be incremented ...

    i mean if i declare something like this,
    Code:
     char *a[10];  
    a++;


    but the code
    Code:
     int main(int argc, char *argv[])
    {
    
    
    printf("%s", *++argv);
    
    
    }
    was running without any compiler error..



    some body please explain this...


    thanks and regards..
    raj_ksrt.

  2. #2
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    a pointer to the base address of an array can be incremented.

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    C++ Witch laserlight's Avatar
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    argv is a pointer to the first element of an array of pointers to char... until you increment it, in which case it becomes a pointer to the second element of the same array of pointers to char.
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    i am puzzled, though.

    if a is an array of char *s, why doesn't the OP's first expression point to the first char * in a?

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    CSharpener vart's Avatar
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    why doesn't the OP's first expression point to the first char * in a
    it does, but it is still array and cannot be incremented
    if its value is assigned to the pointer, or passed as a function parameter - we get the pointer with the same value, pointer can be incremented
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    C++ Witch laserlight's Avatar
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    if a is an array of char *s, why doesn't the OP's first expression point to the first char * in a?
    Because a is an array of pointers to char, not a pointer to the first element of an array of pointers to char. When passed as an argument, an array is converted to a pointer to its first element.
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    Banned master5001's Avatar
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    I am starting to see way more questions such as this on the forums. Perhaps its time to whip up an in depth explanation of the indirection of pointers. I am not surprised this is so complicated to many these days though. I notice schools are leaning heavily on teaching C# and Java to entry level computer science students.

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    Just Lurking Dave_Sinkula's Avatar
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    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by master5001 View Post
    I am starting to see way more questions such as this on the forums. Perhaps its time to whip up an in depth explanation of the indirection of pointers. I am not surprised this is so complicated to many these days though. I notice schools are leaning heavily on teaching C# and Java to entry level computer science students.
    Confusion about pointers is nothing new around here. However, there is indeed an oddity in the language with regard to this particular question. Consider this:

    Code:
    int foo(int *blah[10])
    {
        int *fuzz[10];
        blah++;
        fuzz++;
    }
    Even though the two variables fuzz and blah seem to be declared in EXACTLY the same way, they ARE NOT THE SAME. The increment of blah is allowed. The increment of fuzz is not.

    I do not blame people for having a hard time understanding why.

  10. #10
    Cat without Hat CornedBee's Avatar
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    Which is why I always advertise not using the [] syntax in function arguments. Far less confusing that way.
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    Banned master5001's Avatar
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    >>I do not blame people for having a hard time understanding why.

    I suppose you have a good point on that one. This is one of the reasons iterators were developed.

    >>Which is why I always advertise not using the [] syntax in function arguments. Far less confusing that way.

    Kudos to that...

  12. #12
    C++まいる!Cをこわせ! Elysia's Avatar
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    To add another one to the list:
    http://cpwiki.sourceforge.net/A_pointer_on_pointers

    Though they are so incredibly simple, they can also be mind boggling. One needs to know the basics and work from that, not trying to see pointers like some super powerful, super flexible solution to everything. They work just one way, not multiple ways.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  13. #13
    Banned master5001's Avatar
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    To be honest, I think the problem is that pointers as we know them are based on the programming concepts of C and people learn how to read and think in C++ nowadays. brewbuck's example is not very intuitive for any type of understanding though. I think a lot of benefit could be gained through teaching students about C++'s alternatives (which I never use, despite my advocation of them) to pointers.

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    C++まいる!Cをこわせ! Elysia's Avatar
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    I don't know if I agree. Pointers are still very important, even in C++.
    It's absolutely a good thing to know about pointer basics. My own guess is that books don't cover the basics of pointers (they merely say, if you want another function to modify an argument, then do this - it's called pass by pointer) or they simply do not understand it and skips the basics.
    Or it could be the teachers' fault. We know how many bad teachers are out there.

    And I don't know if people are really thinking C++ these days... I've messed around in a project that is very "C+"! Basically, it heavily utilizes classes but never (or very rarely) uses the standard library. Everything is practically made C.
    C with classes :O
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  15. #15
    Banned master5001's Avatar
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    I am not shirking the importance of pointers. I am simply saying that its not something that seems very well explained to people these days, which is truly unfortunate. And the even more unfortunate thing is that despite not receiving enough information about pointers, they are also not receiving enough information about how to accomplish the tasks that pointers complete.

    I think pointers are best explained graphically. In fact some of the best illustrations I've seen regarding pointers were in an assembler tutorial I read way back in the day that assumed a competent understanding of C. Despite that, the images were something I recognized as useful for someone who "doesn't get pointers."

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