assignment from incompatiable pointer type C

Say I want to read in a list of pages name of max 19 character, e.g. 4 (Number of page) Name1 Name2 Name3 Name4

I am trying to use a global 2D array to store the 开发者_运维知识库page number and page name, I got an error saying assignment from incompatiable pointer type...

Thanks

static int nPages;
static char** pageName;

int main(void){
  scanf(" %d", &nPages);

  pageName = (char *)malloc(nPages*sizeof(char));
  for(int i=0; i < nPages ;i++){
    pageName[i] = (char *)malloc(20*sizeof(char));
    scanf(" %s", pageName[i]);
  }

//Free Memory Here of coz. 

  return 0;
}

Never cast the return value of malloc() in C. It hides compiler warnings that actually help you, and it's never necessary so it just adds clutter. You should use:

pageName = malloc(nPages * sizeof *pageName);

Note how this is free from repetitions of the type name of pageName. Here, sizeof *pageName means "the size of the object pointed at by pageName", i.e. "the size of a character pointer". You should expect a sizeof expression as malloc()'s argument very often.

Also, sizeof (char) is always 1 in C, so that particular expression, it can be argued, adds more clutter than it helps make the code safe.

The problem lies right there:

pageName = (char *)malloc(nPages*sizeof(char));

pageName is a char **, not a char *. So it should read:

pageName = malloc(nPages*sizeof(char*)); // sizeof(char *), and no need to cast

EDIT: removed the cast

Your defined pageName as char ** but when calling malloc to initialize the pointer, you use a cast to (char *). Maybe that is the problem.

You are assigning char* to char** at your first malloc line. Just drop the (char*) cast - C handles void* to char** conversion automatically.

char* and char** are two different types, and you can't freely assign the first to the latter.

Having said that, you have to do a two-step initialization. First, you have to malloc() space for nPages string:

pageName = (char**) malloc(nPages * sizeof(char*));

then, you have to malloc() space for each pageName:

for (i = 0; i < nPages; ++i) {
    pageName[i] = (char*) malloc(20);
}