C File Handling

fopen() Function:

This function is used to open a file. It takes two arguments: the name of the file you want to open and the mode in which you want to open it (e.g., read, write, append, etc.). It returns a file pointer, which is a data structure that allows you to read from or write to the file.

For reading syntax:

FILE *fp = fopen("example.txt", "r");

For writing syntax:

FILE *fp = fopen("example.txt", "w");

The following "mode" are used in data processing:

1. "r" (Read): Open for reading. The file is opened for reading, and if the file doesn't exist, the operation will fail.

2. "w" (Write): Open for writing. If the file exists, it is truncated to zero length. If the file does not exist, a new empty file is created.

3. "a" (Append): Open for writing, but if the file exists, data is appended to the end of it rather than overwriting the existing content. If the file doesn't exist, a new file is created.

4. "rb" (Read Binary): Open for reading in binary mode. Similar to "r", but for binary files.

5. "wb" (Write Binary): Open for writing in binary mode. Similar to "w", but for binary files.

6. "ab" (Append Binary): Open for writing in binary mode with appending. Similar to "a", but for binary files.

7. "r+" (Read/Write): Open for both reading and writing. The file must exist, but you can both read and write to it.

8. "w+" (Write/Read): Open for both reading and writing. If the file exists, it is truncated. If it doesn't exist, a new file is created.

9. "a+" (Append/Read): Open for both reading and writing, with appending. If the file exists, data is appended; if not, a new file is created.

10. "r+b" or "rb+" (Read/Write Binary): Open for both reading and writing in binary mode. Similar to "r+", but for binary files.

11. "w+b" or "wb+" (Write/Read Binary): Open for both reading and writing in binary mode. Similar to "w+", but for binary files.

12. "a+b" or "ab+" (Append/Read Binary): Open for both reading and writing in binary mode with appending. Similar to "a+", but for binary files.

fclose() Function:

This function is used to close a file that was previously opened with 'fopen()'. It takes a single argument, which is the file pointer associated with the file you want to close.

Syntax for closing:

fclose(fp);

feof() Function:

This function is used to check whether the end of a file has been reached. It takes a file pointer as its argument and returns a non-zero value if the end of the file has been reached, or 0 if it hasn't.

Syntax:

if (feof(file)) {
    // End of file has been reached
} else {
    // End of file has not been reached
}

* The 'fread()', 'fwrite()', 'fscanf()', and 'fprintf()' are functions used for file input and output operations. They are part of the standard I/O library and are used for reading from and writing to files. Here's an overview of each function:

fread() Function:

This function is used for reading binary data from a file. It is typically used when you want to read data in its raw binary format. The function takes four arguments: a pointer to a buffer where the data will be stored, the size of each element to be read, the number of elements to read, and a file pointer to the input file.

Syntax:

FILE* file = fopen("data.bin", "rb");
if (file != NULL) {
    int data[10];
    fread(data, sizeof(int), 10, file);
    fclose(file);
}

fwrite() Function:

This function is used for writing binary data to a file. It is the counterpart of 'fread()'. It takes four arguments: a pointer to the data to be written, the size of each element, the number of elements to write, and a file pointer to the output file.

Syntax:

FILE* file = fopen("data.bin", "rb");
if (file != NULL) {
    int data[10];
    fread(data, sizeof(int), 10, file);
    fclose(file);
}

fscanf() Function:

This function is used for reading data from a text file. It allows you to read formatted data from the file based on a specified format string. The function takes a file pointer and format string followed by a list of pointers to variables where the read data will be stored.

Syntax:

FILE* file = fopen("data.txt", "r");
if (file != NULL) {
    int value;
    fscanf(file, "%d", &value);
    fclose(file);
}

fprintf() Function:

This function is used for writing data to a text file, just like printf(). It allows you to format data and write it to the file. The function takes a file pointer and a format string, followed by a list of values to be written to the file based on the format string.

Syntax:

FILE* file = fopen("data.txt", "w");
if (file != NULL) {
    int value = 42;
    fprintf(file, "The value is: %d\n", value);
    fclose(file);
}

#include ＜stdio.h>

int main() {
    FILE *file;
    char ch;

    // Open the file for reading
    file = fopen("example.txt", "r");

    if (file == NULL) {
        printf("Unable to open the file.\n");
        return 1;
    }

    // Read and print characters from the file
    while ((ch = getc(file)) != EOF) {
        printf("%c", ch);
    }

    // Close the file
    fclose(file);

    return 0;
}

The file opened & read successfully.

#include ＜stdio.h>

int main()
{
    char str[] = "Hello, World!";
    FILE *file = fopen("output.txt", "w"); // Open the file for writing

    if (file == NULL)
    {
        perror("Error opening file");
        return 1;
    }

    for(int i; str[i] != '\0'; i++)
    {
        if (putc(str[i], file) == EOF)
        {
            perror("Error writing to file");
            return 1;
        }
    }

    fclose(file); // Close the file

    return 0;
}

int getw(FILE *stream);

#include ＜stdio.h>

int main() {
// Open a binary file for reading
    FILE *file = fopen("data.bin", "rb");
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }

// Read an integer from the file
    int value = getw(file);
    printf("Read value: %d\n", value);

    fclose(file); // Close the file
    return 0;
}

int putw(int w, FILE *stream);

#include ＜stdio.h>

int main() {
    FILE *file = fopen("data.bin", "wb"); // Open a binary file for writing
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }

    int value = 42;
    putw(value, file); // Write an integer to the file

    fclose(file); // Close the file
    return 0;
}