What is iOS App C++?

 What's the difference between ios::ate and ios:app when writing to a file.

In my view, ios::app gives you the ability to move around in the file, whereas with ios::ate it can only read/write at the end of the file. Is this correct?

c++filefstreamc++-standard-library

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edited Jul 17 '19 at 7:02

L. F.

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asked Apr 28 '12 at 1:12

Adam_G

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• By the way, it is really ios_base::ate and ios_base::app. – L. F. Jul 17 '19 at 7:02

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79

It’s the other way around. When ios::ate is set, the initial position will be the end of the file, but you are free to seek thereafter. When ios::app is set, all output operations are performed at the end of the file. Since all writes are implicitly preceded by seeks, there is no way to write elsewhere.

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answered Apr 28 '12 at 1:17

Jon Purdy

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39

They are specified as follows (in 27.5.3.1.4 of C++11):

app seek to end before each write

ate open and seek to end immediately after opening

With ios::app the write position in the file is "sticky" -- all writes are at the end, no matter where you seek.

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edited Jun 20 '20 at 9:12

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answered Apr 28 '12 at 1:16

Steve Jessop

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29

It is pretty good documented here.

ios::ate "sets the stream's position indicator to the end of the stream on opening."

ios::app "set the stream's position indicator to the end of the stream before each output operation."

This means the difference is that ios::ate puts your position to the end of the file when you open it. ios::app instead puts it at the end of the file every time you flush your stream. If for example you two programs that write to the same log file ios::ate will override anything that was added to the file by the other program since your program opened it. ios:app will instead jump to the end of file each time your program adds a log entry.

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edited Jun 14 '20 at 14:50

answered Apr 28 '12 at 1:21

Haatschii

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12

ios::app--> "We cannot move the pointer. It will be only at end."

ios::ate--> "We can move the record pointer to any other place."

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edited May 27 '20 at 16:05

Sina Raoufi

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answered Sep 23 '13 at 10:14

naveen

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1

The ios::ate option is for input and output operations and ios::app allows us to add data to the end of file.