c++ - fopen 函数中的 a 和 a+ 选项有什么区别？

Question

我无法理解 C fopen api 文档中对“a”和“a+”选项的描述。 “a+”中的选项是追加和更新。这里更新这个词是什么意思？

Answer 1

这是手册页 (man fopen) 的内容:

a

Open for appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file.

a+

Open for reading and appending (writing at end of file). The file is created if it does not exist. The initial file position for reading is at the beginning of the file, but output is always appended to the end of the file.

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这意味着:

获得+:指针最初位于文件的开头(用于读取)，但是当尝试进行写操作时，它会移至文件的末尾。