fopen() in C

In C Language, "fopen()" is a function used to open a file.

It's part of the standard input/output library "stdio.h".

This function opens a file and returns a pointer to a "FILE" object which can then be used for subsequent operations on the file.

Syntax:

#include <fcntl.h>

int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);

"filename": This is a C string containing the name of the file to be opened. It can be either an absolute or relative path to the file.

"mode": This is also a C string indicating the opening mode. It specifies how the file should be opened, whether for reading, writing, appending, etc. The modes include:

"r": Open for reading. The file must exist.
"w": Open for writing. If the file exists, its contents are erased. If the file doesn't exist, it's created.
"a": Open for appending (writing at the end of the file). The file is created if it doesn't exist.
"r+": Open for both reading and writing. The file must exist.
"w+": Open for both reading and writing, but the existing contents are erased. If the file doesn't exist, it's created.
"a+": Open for reading and appending. The file is created if it doesn't exist.

fopen Example:

#include <stdio.h>

int main() {
    FILE *fp;

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

    if (fp == NULL) {
        printf("Error opening the file.\n");
        return 1;
    }

    fprintf(fp, "This is a test file.");
    fclose(fp);

    return 0;
}

"example.txt" is the name of the file to be opened, and "w" specifies that it should be opened for writing.
If the file doesn't exist, it will be created.
The function returns a pointer to a "FILE" structure which is then used to write to the file using "fprintf()".
Finally, "fclose()" is used to close the file when done.
Always remember to check if "fopen()" returns "NULL" to handle cases where the file couldn't be opened.

fclose() -->