avstrlcpy

av_strlcpy is a utility function found in FFmpeg’s libavutil library that provides a safe string-copy operation modeled after the BSD strlcpy function. It is used to copy a C string into a fixed-size destination buffer while minimizing the risk of buffer overflows.

The typical signature is: size_t av_strlcpy(char *dst, const char *src, size_t dst_size). The function copies up to dst_size - 1 characters from src into dst, NUL-terminating the result if dst_size is non-zero. It returns the length of the source string (the number of characters it would have copied in a space-unlimited buffer). If the return value is greater than or equal to dst_size, truncation occurred.

Guidance and behavior: If dst_size is 0, av_strlcpy performs no writes but still returns the length of src. This makes it possible to determine the required buffer size before allocation. The function does not attempt to handle overlapping memory regions, and it relies on valid non-null pointers for both dst and src in typical usage.

Usage context: av_strlcpy is used throughout FFmpeg’s codebase to safely populate fixed-size buffers for messages, metadata, and other string data, reducing common errors associated with manual strncpy or snprintf-based copying. It provides consistent semantics across platforms, aiding portability.

See also: strlcpy, av_strlcat.