freopen

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FILE *freopen (const char fileName[], const char mode[], FILE *oldStream);

Purpose

Does the following:

Attempts to close the file that is associated with oldStream—failure to close the file successfully is ignored
Opens a file and associates it with the I/O stream that is pointed to by oldStream
Clears error and end-of-file indicators for the I/O stream

Note This function is useful for redirecting the standard streams (stdin, stdout, stderr) to a file.

If the open operation fails, fopen returns NULL and sets errno to a nonzero value.

Input

Name Type Description

fileName const char [] Specifies the name of the new file that is opened. The I/O stream associated with oldStream is associated with this file.

mode

const char []

Specifies the mode of reading and writing for the opened file. The possible modes are listed in the following chart:

Mode argument	Description
r	Open text file for reading.
w	Truncate to zero length or create text file for writing.
a	Append; open or create text file for writing at end-of-file.
rb	Open binary file for reading.
wb	Truncate to zero length or create binary file for writing.
ab	Append; open or create binary file for writing at end-of-file.
r+	Open text file for reading and writing.
w+	Truncate to zero length or create text file for reading and writing.
a+	Append; open or create text file for reading and appending.
rb+	Open binary file for reading and writing.
wb+	Truncate to zero length or create binary file for reading and writing.
ab+	Append; open or create binary file for reading and appending.

oldStream FILE * Contains a pointer to the I/O stream that is redirected. The file formerly associated with this stream is closed if possible.

Name	Type	Description
newStream	FILE *	Contains a pointer to the new I/O stream associated with the opened file if successful. If the open operation fails, fopen returns NULL and sets errno to a nonzero value.

Library: ANSI C Library

Include file: ansi_c.h

LabWindows/CVI compatibility: LabWindows/CVI 3.0 and later

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