lvalue required as increment operand

Question

gcc 4.4.4

What am I doing wrong?

char x[10];
char y[] = \"Hello\";
while(y != NULL)
    *x++ = *y++;

Many thanks for any advice.

Answer 1

Most likely you fell victim to a popular misconception that "array is a pointer", i.e. when you define an array what you actually get is an ordinary pointer that points to some block of memory allocated somewhere. In your code you are making an attempt to increment that pointer.

The code does not "work" because in reality arrays are not pointers. Arrays are arrays. Arrays cannot be incremented. There's no such operation as "increment an array" in C language. In fact, arrays by themselves in C are non-modifiable lvalues. There are no operations in C that can modify the array itself (only individual elements can be modifiable).

If you want to traverse your arrays using the "sliding pointer" technique (which is what you are actually trying to do), you need to create the pointers explicitly and make them point to the starting elements of your arrays

char *px = x;
char *py = y;

After that you can increment these pointers as much as you want.