What does the FILE* returned by fopen actually point to in C? Consider FILE fp; fp = fopen("trial", "r");
C Programming
Input / Output
Difficulty: Easy
Choose an option
-
AThe first character in the file
-
BA structure which contains a char pointer which points to the first character of a file.
-
CThe name of the file.
-
DThe last character in the file.
Answer
Correct Answer: A structure which contains a char pointer which points to the first character of a file.
Explanation
Introduction / Context:Many beginners think a FILE points directly to file contents. In reality, FILE is an opaque structure managed by the C runtime that holds buffering state, an internal position indicator, and an association with an underlying file descriptor. Understanding this distinction helps avoid misconceptions about pointer arithmetic on FILE* and clarifies how stdio buffering works.
Given Data / Assumptions:
- We use fopen to obtain a FILE* stream pointer.
- Standard I/O buffering and FILE abstraction apply.
- We are not using memory-mapped I/O here.
Concept / Approach:
- FILE* points to a C library structure (opaque to user code).
- That structure typically contains a buffer, status flags, and bookkeeping including a pointer into the buffer and an underlying file descriptor.
- It does not point to the first or last character of the actual file on disk.
Step-by-Step Explanation:
Call fopen("trial","r") → runtime allocates/initializes a FILE object.fp holds the address of that FILE object in memory.The FILE object manages buffered access to file data via getc/putc, fread/fwrite, etc.Verification / Alternative check:
Trying to dereference fp as if it were a char* is a type error; only stdio functions should use it.Why Other Options Are Wrong:
- The first/last character in the file: A FILE* does not point to file contents directly; it is a handle to a stream structure.
- The name of the file: The stream is not a string; it is a structured object.
Common Pitfalls:
- Assuming fp+1 advances in the file; pointer arithmetic on FILE* is invalid.
- Forgetting to close the stream with fclose to flush buffers and release resources.
Final Answer:
A structure which contains a char pointer which points to the first character of a file.