fstream读/写移动文件指针 [英] does fstream read/write move file pointer

问题描述

这是一个简单的问题，我希望可以很容易地回答，做文件流读取和写入操作移动指针吗？例如：

This is kind of a simple question that I hope can be answered easily, do the file stream read and write operations move the pointer along? As an example:

cpos=10000;
for (i=0;i<20;i++) {
   dataFile.seekg(cpos+i,ios::beg);
   dataFile.read(carray[i],1);
}

与逻辑上相同：

dataFile.seekg(cpos,ios::beg);    
cpos=10000;
for (i=0;i<20;i++) {
    dataFile.read(carray[i],1);
}

换句话说，carray []包含相同的内容（我不能看到第一个方法是有效的，所以我希望正确的答案是肯定的）。如果是这样，是写操作显示的相同行为？

In other words, does carray[] contain the same contents regardless of which method is used (I can't see the first method being efficient so I am hoping that the correct answer is yes). If so, is same behavior exhibited by write operations?

推荐答案

是的，这是它的工作方式。你的例子不一样，但。您的第一个示例读取从10000，然后10001，然后10002，等等。第二个需要循环外寻求设置初始位置。为了达到100％的等效性，你需要让你的第二个例子看起来像：

Yes, that is the way it works. Your examples aren't quite the same, though. Your first example reads from 10000, then 10001, then 10002, etc. The second needs a seek outside the loop to set the initial position. To be 100% equivalent, you need to have your second example look like:

cpos=10000;
dataFile.seekg(cpos,ios::beg);
for (i=0;i<20;i++) {
   dataFile.read(carray[i],1);
}

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