Lab 07 - File Handling

In C, files are accessed through file pointers of type FILE *. You open files with fopen() and close them with fclose().

FILE *pFile = fopen("filename.txt", "r");
if (pFile == NULL) {
    printf("Failed to open file\n");
} else {
    // perform I/O operations
    fclose(pFile);
}

int fgetc(FILE *stream)

• reads one character from the given file, returns the character as an unsigned char converted to int, or EOF on end-of-file or error

int fputc(int c, FILE *stream)

• writes a single character to the given file, returns the character written, or EOF on error

int ch;
while ((ch = fgetc(pFile)) != EOF) {
    fputc(ch, outFile);
}

char *fgets(char *str, int size, FILE *stream)

• reads up to size-1 characters or until newline, whichever comes first.

int fputs(const char *str, FILE *stream)

• writes a string to the file (no newline added automatically).

char buffer[100];
while (fgets(buffer, sizeof(buffer), file)) {
    fputs(buffer, stdout);
}

int fscanf(FILE *stream, const char *format, ...)

• reads formatted data

int fprintf(FILE *stream, const char *format, ...)

• writes formatted data

char text[50];
FILE *pFile = fopen("filename.txt", "r");
while (fscanf(pFile, "%s", text) == 1) {
    printf("%s\n", text);
}
fclose(pFile);

size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream)

• reads nmemb elements of size bytes each into memory

size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream)

• writes nmemb elements of size bytes each from memory to file

typedef struct {
    char name[50];
    int age;
} Person;
 
//Write
Person p1 = {"Alice", 25};
FILE *f = fopen("people.dat", "wb");
fwrite(&p1, sizeof(Person), 1, f);
fclose(f);
 
//Read
Person p2;
FILE *f = fopen("people.dat", "rb");
fread(&p2, sizeof(Person), 1, f);
printf("%s is %d\n", p2.name, p2.age);
fclose(f);

1. Open a text file c_poem.txt in read mode
2. Open another file c_poem_censored.txt in write mode
3. Read each character and replace all occurrences of the letter C with *
4. Write the modified text into the output file c_poem_censored.txt

Copy the following text to the c_poem.txt file:

In the realm of code, C stands tall, a robust language, embraced by all. 
With syntax concise, and power untold, it crafts systems, timeless and bold.
Pointers dance in memory's maze, arrays align in structured arrays.
Functions echo, a symphony of logic, in C's embrace, a coder's magic.
From main to end, the journey unfolds, loops and branches, stories untold.
Efficiency reigns in every line, in the heart of C, brilliance aligns.
Header files whisper of libraries vast, A tapestry woven, from present to past.
C, the maestro in the coding symphony, Crafting elegance in binary harmony.
- ChatGPT

1. Open a text file c_poem_censored.txt in read mode
2. Write a program that:
   • reads each line with fgets()
   • prints each read line to stdout using printf(“%s\n”, …)
   • copies the line to a new file copy.txt, using fputs()
3. Experiment with various buffer sizes: 100, 50, 10
   • what happens when a line in the file is longer than the buffer?

1. Create a file contacts.txt
2. Write a program that:
   • uses fscanf() to read names and ages
   • displays each record on screen
   • counts how many people are in the file and prints their average age
3. (optionally) Ask user for input (name and age) using scanf(…) or fscanf(stdin, …) and add new entries to the contacts.txt file using fprintf()

Copy the following text to the contacts.txt file:

Miles 23
Leonardo 31
George 22
Frederique 40
Robin 4
Riccardo 35