====== 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()''.

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

| "r"	| Read an existing file. |
| "w"	| Write: create new or erase existing file. |
| "a"	| Append: add to end, create if missing. |
| "r+"	| Read and write an existing file. |
| "w+"	| Read and write, create new or erase existing. |
| "a+"	| Read and append, create if missing. |
| "rb/wb/ab"	| Same as above but binary mode. |


==== Character I/O ====

<code c>int fgetc(FILE *stream)</code>

  * 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

<code c>int fputc(int c, FILE *stream)</code>
  * writes a **single character** to the given file, returns the character written, or ''EOF'' on error

<code c>
int ch;
while ((ch = fgetc(pFile)) != EOF) {
    fputc(ch, outFile);
}
</code>


==== Line I/O ====

<code c>char *fgets(char *str, int size, FILE *stream)</code>
  * reads up to ''size-1'' characters or until newline, whichever comes first.

<code c>int fputs(const char *str, FILE *stream)</code>
  * writes a string to the file (no newline added automatically).

<code c>
char buffer[100];
while (fgets(buffer, sizeof(buffer), file)) {
    fputs(buffer, stdout);
}
</code>


==== Formatted I/O ====

<code c>int fscanf(FILE *stream, const char *format, ...)</code>

  * reads formatted data

<code c>int fprintf(FILE *stream, const char *format, ...)</code>

  * writes formatted data

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



==== Block (binary) I/O ====

<code c>size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream)</code>
  * reads ''nmemb'' elements of ''size'' bytes each into memory

<code c>size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream)</code>
  * writes ''nmemb'' elements of ''size'' bytes each from memory to file


<code c>
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);


</code>


----


==== Tasks ====

=== Task 1: Text censorship ===

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

Copy the following text to the ''c_poem.txt'' file:
<code>
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
</code>


=== Task 2: Copying ===

  - Open a text file ''c_poem_censored.txt'' in read mode
  - 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()''
  - Experiment with various buffer sizes: 100, 50, 10
    * what happens when a line in the file is longer than the buffer?


=== Task 3: Read and Display Contacts ===

  - Create a file ''contacts.txt''
  - 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
  - //(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:
<code>
Miles 23
Leonardo 31
George 22
Frederique 40
Robin 4
Riccardo 35
</code>