fopen is the standard C function for opening or creating streams. It is primarily used for reading from and writing to files, though there are other uses as well.
Synopsis[]
#include <stdio.h>
FILE *fopen( const char *path,
const char* mode );
Where path can be any valid file path (this is system-depedent), and mode can be any of the following:
- "r" - Opens an existing file for reading. If the file does not exist, the function will fail.
- "r+" - Opens the stream for reading AND writing
- "w" - Open the stream for writing. If the file already exists, it will be erased. If it does not exist, it will be created.
- "w+" - Open the stream for reading AND writing; if the file does not exist, it will be created.
- "a" - Like "w", except that if the file exists new data will be written to the end of the file
- "a+" - Open the stream for reading AND appending
Examples[]
The following example shows how to create a file, "my_file.txt", then write some text to it:
#include <stdio.h> // Standard I/O functions
#include <stdlib.h> // EXIT_SUCCESS and EXIT_FAILURE
int main()
{
FILE* my_file = fopen("my_file.txt", "w"); // Attempt to create "my_file.txt"
if( !my_file ){ // If my_file is NULL, then fopen() failed
fputs("error: could not open my_file.txt for writing\n", stderr);
return EXIT_FAILURE; // Exit unsuccessfully
}
fputs("some text\n", my_file); // Write "some_text" to my_file.txt
fclose(my_file); // Closes the stream and flushes all buffers (writes changes to the file)
return EXIT_SUCCESS;
}