The author discovers a bug in a DOS emulator involving file I/O behavior when combining read and write commands. Through debugging, they identify issues within different C run-time libraries, ultimately finding the root of the problem in the longstanding restrictions on switching read/write directions in C library streams. While some systems allow free intermixing of reads and writes, others require specific precautions to ensure compatibility. Historical analysis reveals the evolution of file I/O functionality in UNIX and early C implementations, shedding light on why the limitations persist in modern standards. The complex nature of file I/O in C highlights the challenges of maintaining backward compatibility across diverse platforms.
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