fopen()中r +和w +之间的区别 [英] Difference between r+ and w+ in fopen()

问题描述

在fopen("myfile", "r+")中，"r+"和"w+"打开模式有什么区别?我读到了:

In fopen("myfile", "r+") what is the difference between the "r+" and "w+" open mode? I read this:

"r"打开一个文本文件以供阅读.
"w"打开一个文本文件进行写入， 将现有文件截断为零长度，或者创建不存在的文件.

"r" Open a text file for reading.
"w" Open a text file for writing, truncating an an existing file to zero length, or creating the file if it does not exist.

"r+"打开一个文本文件进行更新(即，用于读取和读取). 写作).
"w+"打开一个文本文件进行更新(读取和写入)， 首先截断 如果文件存在，则文件长度为零；如果文件不存在，则文件长度为零.

"r+" Open a text file for update (that is, for both reading and writing).
"w+" Open a text file for update (reading and writing), first truncating the file to zero length if it exists or creating the file if it does not exist.

我的意思是区别在于，如果我使用"w+"打开文件，该文件将首先被删除吗?

I mean the difference is that if I open the file with "w+", the file will be erased first?

推荐答案

主要区别在于w+如果文件存在，则将文件截短为零长度；如果不存在，则创建一个新文件.而r+既不删除内容也不创建新文件(如果不存在).

The main difference is w+ truncate the file to zero length if it exists or create a new file if it doesn't. While r+ neither deletes the content nor create a new file if it doesn't exist.

尝试这些代码，您将了解:

Try these codes and you will understand:

#include <stdio.h>
int main()
{
   FILE *fp;

   fp = fopen("test.txt", "w+");
   fprintf(fp, "This is testing for fprintf...\n");
   fputs("This is testing for fputs...\n", fp);
   fclose(fp);
}  

然后是

#include <stdio.h>
int main()
{
   FILE *fp;

   fp = fopen("test.txt", "w+");
   fclose(fp);
}   

然后打开文件test.txt，然后查看会发生什么.您将看到第一个程序写入的所有数据已被删除.
对r+重复此操作并查看结果.希望你能理解.

Then open the file test.txt and see the what happens. You will see that all data written by the first program has been erased.
Repeat this for r+ and see the result. Hope you will understand.

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