c - How to get the string size in bytes?

Question

As the title implies, my question is how to get the size of a string in C. Is it good to use sizeof if I've declared it (the string) in a function without malloc in it? Or, if I've declared it as a pointer? What if I initialized it with malloc? I would like to have an exhaustive response.

Answer 1

You can use strlen. Size is determined by the terminating null-character, so passed string should be valid.

If you want to get size of memory buffer, that contains your string, and you have pointer to it:

• If it is dynamic array(created with malloc), it is impossible to get it size, since compiler doesn't know what pointer is pointing at. (check this)
• If it is static array, you can use sizeof to get its size.

If you are confused about difference between dynamic and static arrays, check this.