将char **分配给char *中的类型不兼容

Question

I have the following bit of code:

As a global variable:

char *orderFiles[10];

And then my main method:

int main(int argc, char *argv[])
{
    orderFiles = argv;
}

However it keeps giving me an error. What am I doing wrong?

Answer 1

It's giving you an error because char *x[10] gives you an array of ten char pointers which is non-modifiable. In other words, you cannot assign to x , nor change it in any way. The equivalent changeable version would be char **orderFiles - you can assign argv to that just fine.

As an aside, you could transfer individual arguments to your array thus:

for (i = 0; i <= argc && i < sizeof(orderFiles)/(sizeof(*orderFiles); i++)
    orderFiles[i] = argv[i];

but that seems rather convoluted. It will either fill up orderFiles with the first N arguments or partially fill it, making the next one NULL.

If your intent is simply to stash away the arguments into a global so that you can reference them anywhere, you should do something like:

#include <stdio.h>

char **orderFiles;
int orderCount;

static void someFn (void) {
    int i;
    printf ("Count = %d\n", orderCount);
    for (i = 0; i < orderCount; i++)
        printf ("%3d: [%s]\n", i, orderFiles[i]);
    // or, without orderCount:
    //    for (i = 0; orderFiles[i] != NULL; i++)
    //        printf ("%3d: [%s]\n", i, orderFiles[i]);
    //    printf ("Count was %d\n", i);

}

int main (int argc, char **argv) {
    orderCount = argc;
    orderFiles = argv;
    someFn();
    return 0;
}

That code saves the arguments into globals so they can be accessed in a different function.

You should save both arguments to main if you want to use argc as well although, technically, it's not necessary since argv[argc] is guaranteed to be NULL for hosted environments - you could use that to detect the end of the argument array.

Answer 2

orderFiles is a const char ** , you can't modify it (the array pointer itself).

You could try assigning the array members (ie orderFiles[0] = argv[0] and so on).

Answer 3

The problem is that there is a difference between arrays initialized without a length, and those initialized with one. Remove the 10 from the global variables declaration, and then it should work

The reason for this is that argv is really just a char* * , but orderFiles is an array of 10 char*.

Answer 4

There is an implicit char** for orderFiles yes, but it's constant because you initialized it to a link time allocated block of memory by specifying the size [10] . You should create a non-constant char** or maybe memcpy from argv to your array.

Answer 5

Like they all said two different data types. In other terms think of it this way: argv is an array of c-strings, and your orderFiles is declared as a single c-string.

So how to assign orderFiles depends on what you're trying to do. I typically iterate through argv to get the arguments passed to the application. Note that argv[0] is the application name.