Modifying an instance of a struct in C

Question

I am programming in C. I have a structure as defined below:

struct toExecute{

const char **argv;

};

In my main command, I declare an instance of this structure as shown:

int main (){

const char *wc[] = { "wc", 0 };

const char *ls[] = { "ls", "-l", 0 };

const char *sort[] = { "sort", 0 };

struct toExecute commandList [] = { {ls}, {wc} };

return forkP (2, commandList);

}

However, I want to change commandList [1] to {sort} without creating a new instance of a structure. So basically, I want to update commandList after I declared it. It seems like everything I try ends up not working for various reasons. My question is, how do I write a line of code that says commandList.agv[1] = sort?

Answer 1

This is a restriction/limitation/inconsistency of C and C++.

In an assignment, the left and right hand side have to have the same type. But initialization is more liberal, although looks like an assignment.

Below are two possibilities that might get you the functionality you want.

#include <stdio.h>

typedef const char **toExecute;

int main (){

const char *wc[] = { "wc", 0 };

const char *ls[] = { "ls", "-l", 0 };

const char *sort[] = { "sort", 0 };

toExecute commandList [] = { {ls}, {wc} };

commandList[1] = sort;

printf("%s\n", commandList[1][0]); // should print "sort"

}

You said that you are programming in C. But if what you have is actually a C++ compiler then the following would also work.

#include <stdio.h>

struct toExecute{

const char **argv;

toExecute(const char **a) {argv = a;}

};

int main (){

const char *wc[] = { "wc", 0 };

const char *ls[] = { "ls", "-l", 0 };

const char *sort[] = { "sort", 0 };

struct toExecute commandList [] = { {ls}, {wc} };

commandList[1] = sort;

printf("%s\n", commandList[1].argv[0]); // should print "sort"

}