Variable length strings

[MTK]

I wanted to make a text editor program in C using ncurses, but I need a way to store the text. I cannot use a fixed array because there is no way to if the file has a few characters or hundreds of lines.

I tried using a char pointer and realloc() every time a character is added or removed, it seems to kind of work but it is a bit quirky and will randomly cause errors. I wonder if you have any ideas or know some sites where I can learn about this?

This is my progress:

char* str_new(char* data)
{
	char* ptr;
	ptr = (char*) malloc((sizeof(char) * (strlen(data) + 1)));
	strcpy(ptr, data);
	return ptr;
}

void str_cat(char* str, char* sub)
{
	str = (char*) realloc(str, sizeof(str) + (sizeof(char) * (strlen(sub) + 1)));
	strcat(str, sub);
}

void str_ins_char(char* str, char sub, int index)
{
	str = (char*) realloc(str, (strlen(str)+2)*sizeof(char));
	int i = strlen(str);
	while(i >= index) {
		str[i+1] = str[i];
		i--;
	}
	str[index] = sub;
}

[Maz]

I did not read through the code, but idea of reallocing for each character is terrible. Realloc is quite a heavy call, it is better to allocate some chunck of memory, and realloc only when bigger chunck is needed. (Eg alloc 1kb - if it's too little, realloc for another 1kb).

Also, remember that realloc may move the contents of memory to some other place, so it is easy to mess things when you assume the enlarged block is starting from same location where smaller block was. Ensure you use enough ** in your function calls, to get the changed startingpoint for allocated block out of the function. (Your str_cat() seems to fail in that).

[MTK]

Figuring out how to make it reallocate every 1024 characters or so does seem like a good idea.

Somehow I can't find anything about the "**" operator, though.

[whiteflags]

I think he means that the dereference operator * can be applied many times, depending on the type.

Anyway that's really neither here nor there, it just depends on how you want to do it. And this sort of thing is a FAQ.

[tabstop]

Figuring out how to make it reallocate every 1024 characters or so does seem like a good idea.

Somehow I can't find anything about the "**" operator, though.

That's because there isn't one. But not only are there char * variables, there are char ** variables, and char *** variables, and .... Since if you want to change a pointer, one star is not enough, you will need to use a char ** variable instead.

[MTK]

You mean that I am only changing a local copy of the pointer and if realloc() chooses the change the location, the pointer isn't changed outside the function?

[Maz]

Basically yes.

[MTK]

So will this change the address of the pointer in main():

void changeptr(int** ptr) //So int** is a pointer to a pointer to an int?
{
  *ptr = NEW_MEM_ADDRS;
}

int main()
{
  int* ptr;
  changeptr(ptr);
  return 0;
}

[Maz]

yes.

[robwhit]

changeptr(&ptr);