Nullterminering

Nullterminering, or the null terminator, is a method for marking the end of a string in several programming languages, most notably C. A null-terminated string is stored as a contiguous sequence of characters followed by a terminator byte with the value zero. The terminator allows string-handling routines to determine where the string ends without storing an explicit length.

In memory, the string "hello" is represented as the bytes h, e, l, l, o, followed by a zero byte. Because no separate length field is kept, functions that operate on such strings must scan the data until they encounter the zero terminator to measure length or detect the end of the string.

Null-terminated strings are central to C and C++ and are used in many system interfaces and libraries that interact with C code. This design simplifies memory management and makes it easy to pass strings across language boundaries that expect C-style strings. However, it also introduces risks. Operations such as copying, concatenation, or measurement rely on the terminator and can cause buffer overflows or overreads if the destination buffer is too small or if the terminator is missing. Commonly used functions include strcpy, strcat, and strlen, which can be unsafe if not carefully controlled. Safe alternatives, or bounds-checked versions like strnlen and strncpy, help mitigate these issues.

In modern programming, null-terminated strings remain prevalent mainly for compatibility and low-level interfaces, while higher-level languages often use length-prefixed or managed string representations to avoid these termination vulnerabilities.