Introduction / Context:
Standard I/O in C provides buffered FILE* streams, while lower-level system calls use integer file descriptors (often called handles on some platforms). The fileno function bridges these layers by retrieving the underlying descriptor from a FILE* stream, which can be useful for system-level operations.
Given Data / Assumptions:
- The code opens a file with fopen and obtains a FILE* named fp.
- t = fileno(fp); is evaluated.
- We assume a successful fopen and a standard C library where fileno is available.
Concept / Approach:
- fileno(FILE stream) returns the integer file descriptor associated with the given stream.
- This descriptor is used by low-level I/O functions like read, write, or by OS-specific APIs.
- It is not the size of the file and is not an undefined garbage value when fp is valid.
Step-by-Step Solution:
Call fopen → receive a valid FILE (fp).Call fileno(fp) → get integer descriptor tied to fp.Assign to t → t now holds the OS file handle/file descriptor number.
Verification / Alternative check:
Printing t typically shows small integers (e.g., 3, 4, 5) corresponding to descriptors opened by the process.
Why Other Options Are Wrong:
- File size: fileno does not compute sizes; use fseek/ftell or stat for that.
- Garbage value: Only if fp were invalid; with a valid stream, the descriptor is meaningful.
- Error in fileno(): Not when called correctly with a valid stream.
Common Pitfalls:
- Using fileno portably across platforms requires care; names differ on some systems.
- Mixing buffered stdio with unbuffered system calls can require explicit fflush/fsync.
Final Answer:
The handle associated with "DUMMY.C" file
Discussion & Comments