Fail to create a .txt file and write to it in C++?

Question

Inside one of my functions that are being called by the main(), I have the following very simple testing snippet.

ofstream outFile;
outFile.open("C:\\Program Files\\data\\test.txt");
outFile << "test\n";
outFile.close();

After running the code, I didn't see the file appears. Why is it so?

@villekulla I suppose so, because my other parts are also writing. They are doing it ok. — Sibbs Gambling, Oct 09 '13 at 13:57
@perfectionm1ng yes, it matters, try: `"C:\\\"Program Files\"\\data\\test.txt"` — PaperBirdMaster, Oct 09 '13 at 14:02
@PaperBirdMaster: You are actively wrong. Spaces in filenames matter when passed to an interface that will split on space like calling system command. And you can only use quotes if the interface interprets them. The `CreateFile` interface underlying `ofstream` does neither, therefore the path **MUST NOT CONTAIN QUOTES** (and may contain spaces whatever it wants). — Jan Hudec, Oct 09 '13 at 14:05
Do you have permission to write in that location? By default I think that the whole area under "Program files" is set up to only allow writes by administrators — jcoder, Oct 09 '13 at 14:05
Try to write the file to the location something like C:\Temp or User Temp where you are sure that you can write to — jaklucky, Oct 09 '13 at 14:21
@JanHudec Ok, this explains why i must write `cd "Program Files"` on my system command (thanks for poiting me and the rest of readers on the right direction) but it isn't explaining why the file isnt writed :( — PaperBirdMaster, Oct 09 '13 at 14:21
@PaperBirdMaster: The file almost certainly isn't being written because of permissions. The "user access control" only works in some cases and not others. — Jan Hudec, Oct 09 '13 at 14:27

score 3 · Accepted Answer · edited May 23 '17 at 12:21

3

Unfortunately C++ does not specify any way to get more detailed error. See Get std::fstream failure error messages and/or exceptions.

But the platform-specific interface should work. After each operation check whether outFile.bad() and if it is true, check GetLastError(). Interpret according to appropriate table in documentation or using FormatMessage.

I would suspect the problem is permissions. Windows Vista introduced this "user access control" that should pop up a dialog whenever program wants to do something that requires administrator privileges even if the current user has them. The problem is that the dialog only pops up under certain conditions. Notably it will not pop up for console applications and the application is denied permissions right away. Such application has to be explicitly executed "as administrator". Of course don't forget being able to write particular file there does not imply being able to create a new one.

edited May 23 '17 at 12:21

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answered Oct 09 '13 at 14:09

Jan Hudec

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On Windows, what is the status of `errno`? Does it give you less (more?) information than `GetLastError()`? It would be nice to use it as a platform-independent alternative. But I don't know if `strerror_r` exists on Windows (since I don't think `strerror_s` exists on Unix). – Adrian Ratnapala Oct 09 '13 at 14:37
@AdrianRatnapala: IIRC `GetLastError()` distinguishes some cases that `errno` does not. And `errno` is implemented in terms of `GetLastError()` on windows anyway. – Jan Hudec Oct 09 '13 at 14:45
Does that mean that if I wanted to write something cross-platform, then using `errno` only would not suck very much? Appart from the `strerror_[rs]` issue that is. – Adrian Ratnapala Oct 09 '13 at 20:01
@AdrianRatnapala: I believe errno should do, yes, but I have not tried it myself (I am working on cross-platform application, but we have platform-specific code using native windows APIs, also because windows was first platform and because WinCE don't have the unix APIs). – Jan Hudec Oct 10 '13 at 05:36

Fail to create a .txt file and write to it in C++?

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