Format
#include <stdio.h>
FILE *freopen(const char *filename, const char *mode, FILE *stream);Language Level: ANSI
Threadsafe: Yes.
Description
The freopen() function closes the file that is currently associated with stream and reassigns stream to the file that is specified by filename. The freopen() function opens the new file associated with stream with the given mode, which is a character string specifying the type of access requested for the file. You can also use the freopen() function to redirect the standard stream files stdin, stdout, and stderr to files that you specify.
For database files, if filename is an empty string, the freopen() function closes and reopens the stream to the new open mode, rather than reassigning it to a new file or device. You can use the freopen() function with no file name specified to change the mode of a standard stream from text to binary without redirecting the stream, for example:
fp = freopen("", "rb", stdin);You can use the same method to change the mode from binary back to text.
You cannot use the freopen() function with filename as an empty string in modules created with SYSIFCOPT(*IFSIO).
Return Value
The freopen() function returns a pointer to the newly opened stream. If an error occurs, the freopen() function closes the original file and returns a NULL pointer value.
The value of errno can be set to:
Example that uses freopen()
This example closes the stream1 data stream and reassigns its stream pointer. stream1 and stream2 will have the same value, but they will not necessarily have the same value as stream.
#include <stdio.h>
#define MAX_LEN 100
int main(void)
{
FILE *stream, *stream1, *stream2;
char line[MAX_LEN], *result;
int i;
stream = fopen("mylib/myfile","r");
if ((result = fgets(line,MAX_LEN,stream)) != NULL)
printf("The string is %s\n", result);
/* Change all spaces in the line to '*'. */
for (i=0; i<=sizeof(line); i++)
if (line[i] == ' ')
line[i] = '*';
stream1 = stream;
stream2 = freopen("", "w+", stream1);
fputs( line, stream2 );
fclose( stream2);
}Related Information