FCLOSE一个文件，该文件是已经FCLOSE [英] Fclose a file that is already fclose

问题描述

在我PROGRAMM我可以关闭一个文件，是已经接近。什么时候我在文件上做了 FCLOSE 发生已经接近？

In my programm I may close a file that is already close. What happen when I do a fclose on a file already close ?

如果你不能这样做，怎么知道，如果一个文件被关闭或打开？

And if you can't do so, how to know if a file is closed or open ?

推荐答案

调用 FCLOSE 具有相同的流两次是未定义的行为 - 最有可能崩溃。有没有办法检查 FILE * 已经已经关闭，所以安全的解决方案是，只要它是封闭的指针设置为NULL：

Calling fclose twice with the same stream is undefined behaviour - most likely crash. There is no way to check if FILE* has been closed already, so the safe solution is to set pointer to NULL as soon as it is closed:

fclose(fh);
fh = NULL;

来源：一个指向一个文件对象的值是不确定的相关文件关闭后（C标准草案）。 的号召，FCLOSE（）后，任何使用流会导致未定义的行为。 （单一UNIX®规格）。

Sources: "The value of a pointer to a FILE object is indeterminate after the associated file is closed" (C draft standard). "After the call to fclose(), any use of stream causes undefined behaviour." (The Single UNIX ® Specification).

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