How do i make an array of pointers for execvp

This is a discussion on How do i make an array of pointers for execvp within the C Programming forums, part of the General Programming Boards category; I am trying to use the execvp command and require an array of pointers for the 2nd argument. I am ...

  1. #1
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    How do i make an array of pointers for execvp

    I am trying to use the execvp command and require an array of pointers for the 2nd argument.
    I am storing the arguments in an array of strings. How would I turn that array of strings into an array of pointers?

    Also, how can I terminate the array of pointers with a null pointer.

    I was using the array of strings in the execvp 2nd argument but that was throwing errors and I was trying to make the last entry of the array a null pointer, using strcat and strcpy but both didn't work.

  2. #2
    Registered User claudiu's Avatar
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    type **array_of_pointers;
    array_of_pointers = malloc(NR_POINTERS * sizeof(type*));
    1. Get rid of gets(). Never ever ever use it again. Replace it with fgets() and use that instead.
    2. Get rid of void main and replace it with int main(void) and return 0 at the end of the function.
    3. Get rid of conio.h and other antiquated DOS crap headers.
    4. Don't cast the return value of malloc, even if you always always always make sure that stdlib.h is included.

  3. #3
    ATH0 quzah's Avatar
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    The first hit for exec: Splitting a space delimited string

    But that's assuming you know how to click search and type a word, and click another button or two. I know, I know, it's asking a lot of you.


    Quzah.
    Hope is the first step on the road to disappointment.

  4. #4
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    Sorry, I forgot to use the search function here. Was just googling.

    Some questions about your code for storing from that thread.

    Code:
    char **args = NULL;
    int argcount = 0;
    
    while input
        pop a word off into a buffer
        char **temp;
        temp = realloc( args, 1 + argcount * sizeof *temp )
        if( temp )
        {
            args = temp;
            args[ argcount ] = malloc strlen buf + 1 
            if( args[ argcount ] )
                strcpy( args[ argcount ], buffer )
            argcount++;
        }
    realloc again, adding room for a NULL ptr, or do it at the start, before the loop
    Do you need a (char *) before realloc? I couldn't really understand this line from the man page on realloc.
    The type of this pointer is void*, which can be cast to the desired type of data pointer in order to be dereferenceable.
    Also, how would you add a NULL ptr in?

    Strcpy does not let you put NULL as an argument.

  5. #5
    ATH0 quzah's Avatar
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    Just assign the last pointer NULL:
    Code:
    args[ lastspot ] = NULL;

    Quzah.
    Hope is the first step on the road to disappointment.

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