std::freopen

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< cpp | io | c
 
C++
 
Input/output library
 
C-style I/O
 
Defined in header <cstdio>
FILE *freopen( const char *filename, const char *mode, FILE *stream );

Reassigns an existing file stream stream to a different file identified by filenameusing specified mode. mode is used to determine the new file access mode.

Contents

[edit] Parameters

filename - file name to associate the file stream to
mode - null-terminated character string determining new file access mode
File access
mode string 		Meaning Explanation Action if file
already exists 		Action if file
does not exist
"r" read Open a file for reading read from start failure to open
"w" write Create a file for writing destroy contents create new
"a" append Append to a file write to end create new
"r+" read extended Open a file for read/write read from start error
"w+" write extended Create a file for read/write destroy contents create new
"a+" append extended Open a file for read/write write to end create new
File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has effect only on Windows systems.
On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.
stream - the file stream to modify

[edit] Return value

stream on success, NULL on failure

[edit] Example

The following code redirects stdout to a file

run this code
#include <cstdio>
 
int main()
{
    std::printf("stdout is printed to console");
    std::freopen("redir.txt", "w", stdout);
    std::printf("stdout is redirected to a file")
    std::fclose(stdout);
}

Output: 

stdout is printed to console

[edit] See also

opens a file
(function)
closes a file
(function)
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