Putcharunlocked

Putchar_unlocked is a non-portable variant of the C standard library function putchar. It writes a single character to stdout without performing the locking that protects stdout in multi-threaded environments. This can yield better performance in tight I/O loops when the program runs in a single thread or when external synchronization guarantees safe access to stdout.

Prototype and behavior: int putchar_unlocked(int ch); The function outputs the character corresponding to ch to stdout and returns the written character as an unsigned char converted to int on success, or EOF on error. It does not flush stdout or modify other streams.

Availability and portability: Putchar_unlocked is not part of the ISO C standard. It is provided as a GNU C library (glibc) extension and is available on many Unix-like systems, including Linux and some BSD variants. It is not guaranteed to exist on all platforms or toolchains, such as some Windows environments using MSVC. For portable code, rely on the standard putchar or use unlocked variants only if the target platform provides them and external synchronization is ensured.

Usage considerations: Because putchar_unlocked bypasses lock protection, it is not thread-safe. Its use is appropriate only when stdout is not being written to concurrently by other threads or when the programmer provides external synchronization. In multi-threaded programs or portable code, prefer the standard I/O functions or explicit locking around critical sections.

See also: putchar, getchar_unlocked, putc_unlocked, fputc_unlocked.