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Questions tagged [fflush]

The C standard library `fflush` is used to synchronize the stream on which it is invoked with the actual content of the corresponding file. It can be used only on output streams. A similar function is defined in C++ as `std::fflush`.

The C standard library function fflush function is defined in the <stdio.h> header and its documentation can be found here.

The corresponding C++ standard library function std::fflush is defined in <cstdio> header and documented here.

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Difference between int fpurge() and int fflush() in C

Can anyone please explain me about difference between fpurge(FILE *stream) and fflush(FILE *stream) in C? Both fflush() and fpurge() will discard any unwritten or unread data in the buffer. Please explain me the exact difference between these two…
c.monica
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How fo force subprocess to refresh stdout buffer?

Platform: windows 8.1 IDE: vs2013 use c/c++ Process A read stdout of subprocess using pipe redirect. but subprocess dont invoke fflush after printf, so processs A cant read anything from pipe before subprocess run to end. ps: I have souce code of…
dfdqzp
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Output not printing without fflush(stdout)

I don't understand why sometimes I need to use fflush() and sometimes not. My program is segfaulting at the moment and I am debugging it with print statements. When a program segfaults, does stdout not flush its buffer automatically?
darksky
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Why we flush a stream but not a buffer?

I know this is gonna be quite a stupid question, but after reading so many document about the whole "buffer" system, I can't understand why would people flush a stream but not a buffer. I have seen people write thing like this: FILE*…
walkerlala
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c language scanf - fflush(stdin) - doesnt work

When I use scanf more than one time the program do not wait for another input. Instead it exits I learned that I could put a blank space before the conversion specifier in the scanf-function - yes that solved the problem and I guess that has to do…
java
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Force write of a file to disk

I'm currently implementing a ping/pong buffering scheme to safely write a file to disk. I'm using C++/Boost on a Linux/CentOS machine. Now I'm facing the problem to force the actual write of the file to disk. Is it possible to do so irrespective of…
Gianluca Ghettini
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why use fflush after printf when printf can print by itself?

I'm new to C, sorry if my question is too basic.I often see code like: printf("%d", counter); fflush(stdout); my guess is that it won't print output if the buffer is not full therefore you need to flush the stdout. But I tried to not use fflush,…
user11224591
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Is using fflush(stdout) as fprintf() argument safe?

To I came upon this line of code: fprintf(stdout, "message", fflush(stdout)); Note that the message does not contain any %-tag. Is that safe in visual c++? fflush() returns 0 on success and EOF on failure. What will fprintf() do with this extra…
jumar
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Difference between fflush(stdin) and flushstdin()

What is the difference between using fflush(stdin) and flushstdin()? The only difference I know is that I need to write that void stuff before using flushstdin(), but I don't know why. void flushstdin() { int c; while((c = getchar()) != '\n'…
Rafael Moura
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Do `fseek`, `fsetpos`, and `rewind` flush the buffer in C?

The C reference states that a FILE* opened in update mode ('+') needs to take the following two precautions: Output cannot be followed by input without a call to one of fflush, fseek, fsetpos, or rewind. Input cannot be followed by output wihout a…
Telescope
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what is the different of using fflush(stdout) and not using it

#include int main() { printf("Hello"); fflush(stdout); return 0; } #include int main() { printf("Hello"); return 0; } I'm trying to understand the use of fflush(stdout) and what is the difference between the 2…
Kain
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why fclose() is not always flushing the data to the disk?

I'm getting some weird results, while trying to write data to files in C.
I thought that fclose() closes the *FILE and flushes the data from its buffer to the file.
But for some reason it only flushes the data in my program sometimes and…
piet_lu
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Last element is missing from the 2D array

Code: #include int main(){ int num; scanf("%d", &num); printf("Enter: "); char nums[5][num], ch; for(int i = 0; i < num; i++){ for(int j = 0; j < 5; j++){ if((ch = getchar()) != '\n'){ …
sarwar47
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Do I need to flush named pipes?

I cannot find whether named pipes are buffered, hence the question. The manpage says https://linux.die.net/man/3/mkfifo: A FIFO special file is similar to a pipe ... any process can open it for reading or writing, in the same way as an ordinary…
rph
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What does fflush() do in terms of dangling pointers?

I came across this page that illustrates common ways in which dangling pointes are created. The code below is used to illustrate dangling pointers by returning address of a local variable: // The pointer pointing to local variable becomes //…
Arpith
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