C Pointers and Arrays Incompatible Types

Question

So I was wondering why I can't do this.

int main(int argc, char **argv){

    FILE *src;
    char filePath[261];
    filePath = argv[1];

The last line is where there is a compiler error. What's the difference between char[] and char*? How would I fix this code so I can set filePath equal to argv[1]. Thanks in advance.

This is the difference between the two: http://stackoverflow.com/questions/12676402/why-cant-i-treat-an-array-like-a-pointer-in-c/12676404#12676404 — Mike, Oct 01 '12 at 23:21

score 5 · Answer 1 · answered Oct 01 '12 at 22:52

Use

strcpy(filePath, argv[1]);

and live happy. Don't forget to check argv[1] for being NULL and don't forget to see if argc is > 1.

Your filePath variable is a fixed-size array which is allocated on the stack and argv[i] is a pointer to some memory in the heap. Assigning to filePath cannot be done, because filePath is not a pointer, it is the data itself.

score 2 · Answer 2 · answered Oct 01 '12 at 22:52

2

Because filePath is an array and it's not allowed to modify the address of an array in C. You can use the string family to copy the strings.

answered Oct 01 '12 at 22:52

P.P

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score 1 · Answer 3 · answered Oct 01 '12 at 22:52

You need to have:

FILE *src;
char *filePath;
filePath = argv[1];

since filePath must point to argv, not to an array of 261 bytes. If you want, you can copy the argumenti into the array:

FILE *src;
char filePath[261];
strcpy(filePath, argv[1]);

or better, to avoid risking copying more bytes than you have available (which would result in disaster):

FILE *src;
char filePath[261];
strncpy(filePath, argv[1], sizeof(filePath));

or again

#define MAX_FILESIZE    261

FILE *src;
char filePath[MAX_FILESIZE];
strncpy(filePath, argv[1], MAX_FILESIZE);

score 1 · Answer 4 · answered Oct 01 '12 at 22:58

Q: What's the difference between char[] and char*?

A: Often times, you can use them interchangeably.

But here, you're "attempting to use an array name as an lvalue" :)

Here's a good explanation:

http://eli.thegreenplace.net/2011/12/15/understanding-lvalues-and-rvalues-in-c-and-c/

Here's a short summary of "what's legal, and what's not":

http://msdn.microsoft.com/en-us/library/bkbs2cds.aspx

C Pointers and Arrays Incompatible Types

4 Answers4