Module 14: File Handling & Persistent Stream I/O

1. FILE Streams & Modes 1 / 4

FILE Pointers & fopen Modes

Opening, reading, writing, and closing streams safely

Mode	Action	File Must Exist?	Starting Position
`"r"`	Read text file	Yes (fails if missing)	Beginning of file
`"w"`	Write text file (Overwrites / Truncates to 0)	No (created if missing)	Beginning of file
`"a"`	Append text file (Preserves old contents)	No (created if missing)	End of file
`"rb"` / `"wb"`	Read / Write Binary files (No newline translation)	Same as text	Beginning of file
`"r+"` / `"w+"`	Read and Write (Update mode)	Yes / No	Beginning of file

2. Binary I/O 2 / 4

Binary Block I/O: fread & fwrite

Fast direct memory-to-disk streaming

binary_io.c

typedef struct { uint32_t id; char name[32]; } Record;

Record data[2] = {{1, "Alpha"}, {2, "Beta"}};

// Writing directly from RAM to disk:
FILE *fp = fopen("records.bin", "wb");
if (fp != NULL) {
    fwrite(data, sizeof(Record), 2, fp);
    fclose(fp);
}

3. Random Access 3 / 4

Random File Access: fseek, ftell & rewind

Instant O(1) positioning anywhere inside giant files

file_seeking.c

// 1. Jump to 10th record:
fseek(fp, 10 * sizeof(Record), SEEK_SET);

// 2. Compute total file size in bytes:
fseek(fp, 0, SEEK_END);
long total_bytes = ftell(fp);

// 3. Reset file pointer back to start:
rewind(fp);

4. Error Handling 4 / 4

Error Handling & EOF Detection

feof, ferror, perror, and strerror(errno)

file_errors.c

FILE *fp = fopen("/nonexistent/file.txt", "r");
if (fp == NULL) {
    // Prints: "File Open Error: No such file or directory"
    perror("File Open Error");
    return 1;
}

Module 14: File Handling & Persistent Stream I/O

FILE Pointers & fopen Modes

Binary Block I/O: fread & fwrite

Random File Access: fseek, ftell & rewind

Error Handling & EOF Detection

1. Text vs Binary Files: The Newline Translation Issue

2. Practice Exercises & Solutions