C Programming

FILE INPUT/OUTPUT
To work with files, the library routines must be included into your programs. This is done by the statement,


	#include <stdio.h>

as the first statement of your program.


USING FILES


The following illustrates the fopen function, and adds testing to see if the file was opened successfully.


	#include <stdio.h>
	/* declares pointers to an input file, and the fopen function */
	FILE   *input_file, *fopen ();

	/* the pointer of the input file is assigned the value returned from the fopen call. */
	/* fopen tries to open a file called datain for read only. Note that */
	/* "w" = write, and "a" = append.  */
	input_file = fopen("datain", "r");

	/* The pointer is now checked. If the file was opened, it will point to the first */
	/* character of the file. If not, it will contain a NULL or 0. */
	if( input_file == NULL ) {
		printf("*** datain could not be opened.\n");
		printf("returning to dos.\n");
		exit(1);
	}


NOTE: Consider the following statement, which combines the opening of the file and its test to see if it was successfully opened into a single statement.


	if(( input_file = fopen ("datain", "r" )) == NULL ) {
		printf("*** datain could not be opened.\n");
		printf("returning to dos.\n");
		exit(1);
	}


ęCopyright B Brown. 1984-1999. All rights reserved.