Why is a null terminator necessary?

Question

I've been teaching myself c++ for the last couple days to prepare for my freshman year as a CS major. I'm on C-style strings right now, and wondering what the point of a null terminator is.

I understand that it's necessary, but I guess I just don't fundamentally understand why a string wouldn't just end on its last char.

Answer 1

I just don't fundamentally understand why a string wouldn't just end on its last char.

There are several ways of knowing where is the "last char":

1. Store the number of characters in the string separately from the string's characters,
2. Put a marker that indicates the last char of the string, or
3. Store the pointer to the last char of the string separately from the string's characters.

C choose the second route; other languages (Pascal, etc.) choose the first route. Some implementations of C++ std::string choose the third route^* .

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^* Even std::string implementations that use the first or the third approach null-terminate their buffers for compatibility with the C portions of the library. This is necessary to ensure that c_str() returns a valid C string.

Answer 2

In C and C++, c-strings are stored in a character array. To allow strings of different lengths, these arrays are often allocated much larger than the actual strings they are to contain. For example, a programmer may allocate a char[256] array, which can hold a string with a length anywhere between 0 characters and 255. But the computer has to be able to know exactly how long the string actually is, so it must end with a null character. Otherwise, it would be neccessary for the character array length to be exactly the same as the string (an impractical solution, as allocating and copying memory uses a lot of resources).