when i would use char *argv[] and when char** argv[] ?

This is a discussion on when i would use char *argv[] and when char** argv[] ? within the C Programming forums, part of the General Programming Boards category; when i would use char *argv[] and when char** argv[] ? int main(int argc,char * argv[] ) AND int main(int ...

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    Lightbulb when i would use char *argv[] and when char** argv[] ?

    when i would use char *argv[] and when char** argv[] ?

    int main(int argc,char * argv[] )

    AND

    int main(int argc, char** argv[])


    question1 . which one is correct ? what is the difference between them ?


    question 2 say, i am passing command line "this is a test" .....which one i shold use ?

    i have seen both of these two function, so i want to know the difference.

    thanks
    blue_gene

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    correct:
    int main(int argc, char *argv[])

    correct:
    int main(int argc, char **argv)

    incorrect:
    Anything else. (the variable names can be anything you want though). I think there is a third variable sometimes too. Hmm.

    Try this:
    Code:
    #include <stdio.h>
    
    int main(int argc, char *argv[])
    {
    	int i;
    	for (i = 1; i < argc; i++) {
    		printf("%s ", argv[i]);
    	}
    	printf("\n");
    	return 0;
    }
    argc contains the number of arguments (plus 1 for the filename)
    argv[0] is the name of your program. argv[1], argv[2], etc, are the command line arguments you gave.
    Last edited by Brian; 04-14-2004 at 06:30 AM.

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    can you give examples when do i use those two ? as i have asked in my question 2
    blue_gene

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    Quote Originally Posted by blue_gene
    can you give examples when do i use those two ? as i have asked in my question 2
    example added to my original reply. (and edited again because I made a mistake)
    Last edited by Brian; 04-14-2004 at 06:19 AM.

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    ohh...sorrry, it was not loaded fully that time...let me look at it
    blue_gene

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    i understand char * argv[] as array of strings.

    so argv[0] = first string

    argv[1] = second string

    .....so on


    but what is the meaning of char** argv . is it also array of strings ? how do i use in this case ?
    blue_gene

  7. #7
    C++ Developer XSquared's Avatar
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    >is it also array of strings ?
    Yes.

    > how do i use in this case ?
    The same way as char *argv[].
    Naturally I didn't feel inspired enough to read all the links for you, since I already slaved away for long hours under a blistering sun pressing the search button after typing four whole words! - Quzah

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    If you want to pass numbers, you are going to have to convert the string to a number. e.g.

    Code:
    #include <stdio.h>
    /* addprog.c - prints the sum of two numbers
        passed as command line arguments */
    
    int main(int argc, char *argv[])
    {
    	int first, last;
    	if (argc != 3) {
    		printf("Usage: addprog <number1> <number2>");
    		
    		getchar();
    		return 0;
    	}
    	
    	first = atoi(argv[1]);  /* Converts string to an integer */
    	last = atoi(argv[2]);
    	
    	printf("%d", first + last);
    	
    	getchar();
    	return 0;
    }

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    in the second syntax , i think i will get an advantage directly as it is 2-d

    so argv[0][0]--->1 st char of 1 string

    argv[0][1]----> ist char of ist string


    like this...


    but if i write using first syntax, then it is difficult to extract chars this way.


    so, when i need chars from the string i should use 2nd syntx.

    and when i need only strings i should use 1st syntx......something like this, i believe
    blue_gene

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    Quote Originally Posted by blue_gene
    in the second syntax , i think i will get an advantage directly as it is 2-d

    so argv[0][0]--->1 st char of 1 string

    argv[0][1]----> ist char of ist string


    like this...


    but if i write using first syntax, then it is difficult to extract chars this way.


    so, when i need chars from the string i should use 2nd syntx.

    and when i need only strings i should use 1st syntx......something like this, i believe
    I always use *argv[]. It's the one most people use, and it also has the advantage you said of extracting characters.

    EDIT: no wait you can do argv[x][y] on both types. Silly me.
    Last edited by Brian; 04-14-2004 at 06:37 AM.

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    ok, i see,

    hi brian, i wonder how are making corrections/ changes in the page that you have posted already !!

    i dont see any EDIT button here at reply thread.
    blue_gene

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    ohh..sorry, i got it ..its ok.

    thanks
    blue_gene

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    laffo.

  14. #14
    Code Goddess Prelude's Avatar
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    >in the second syntax , i think i will get an advantage directly as it is 2-d
    There is no difference between the two:
    Code:
    char *argv[]
    and
    Code:
    char **argv
    are equivalent. They both mean the same thing and are used the same way, so neither is advantageous over the other. Use whichever you find to be less confusing.
    My best code is written with the delete key.

  15. #15
    Registered User linuxdude's Avatar
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    the title of the original post had this

    char**argv[] !!, that is wrong, that is a 3 dimensional array, not what you want and shouldn't compile. Also, in the first response, someone mentioned a third argument, this is sometimes environment variables, like in linux $(HOME), etc. I can't remember the syntax, I think like this
    char *envp[], right after *argv[].

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