When you pass NULL as the stream argument, the function attempts to dereference that pointer to access the file buffer or file descriptor. Since NULL points to a restricted memory address, the operating system immediately kills the process with a . 2. Common Scenarios for Null Stream Errors
FILE *fptr = fopen("non_existent_file.txt", "r"); // If the file didn't open, fptr is NULL. // The next line will crash the program: fscanf(fptr, "%s", buffer); Use code with caution. Copied to clipboard 3. The "Expression" and Return Value Fscanf C Expression Stream Null
In C, fscanf is an expression that evaluates to an int . Understanding this value is critical for handling streams safely: When you pass NULL as the stream argument,
If the stream is NULL , fscanf doesn't return EOF ; it crashes. You must check the stream before it becomes part of the fscanf expression. 4. Best Practices for Stream Safety Common Scenarios for Null Stream Errors FILE *fptr
Always verify your FILE * pointer immediately after fopen . Defensive programming is the only way to prevent a null stream from breaking your application.