Nullterminator

A null terminator is a sentinel value used to indicate the end of a string or array. In the C family of languages, the terminator is the character '\0'—the ASCII NUL character with value 0. C-style strings consist of a sequence of bytes followed by this null byte, which marks the end of the string in memory.

How it works: A string literal such as "hello" compiles to the bytes h, e, l, l, o, '\0'. Standard library functions like strlen, strcpy, strcat, and printf rely on the presence of the terminator to determine the end of the string. The perceived length of a string is the number of characters before the first '\0'. The terminator is not considered part of the string’s length.

Safety considerations: When allocating storage for a C-style string, space must be reserved for the terminator. If the terminator is missing or overwritten, programs may read beyond the intended end, leading to undefined behavior, crashes, or security vulnerabilities. This issue is prominent in manual buffer handling and string concatenation. For wide-character strings, the terminator is L'\0', and corresponding wide APIs (such as wcslen) apply.

Language variants: Some languages or APIs use length-prefixed strings that store the length explicitly and do not require a terminator. In modern C++, std::string manages length internally and does not rely on a trailing null terminator for common operations, though data may be null-terminated for compatibility with C interfaces. Interoperability with C and many OS APIs often preserves null-terminated strings.

History and usage: The concept originates in C and Unix traditions, with ASCII NUL as a universal terminator in many systems. While still common in systems programming and API design, alternative string representations exist that avoid terminators to enable direct length access.

---