C语言 fopen() 中 r+ 和 w+ 的区别
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Difference between r+ and w+ in fopen()
提问by yaylitzis
In fopen("myfile", "r+")what is the difference between the "r+"and "w+"open mode? I read this:
在fopen("myfile", "r+")什么之间的区别"r+"和"w+"开放模式？我读到这个：
"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+"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.
"r"打开一个文本文件进行阅读。"w"打开文本文件以进行写入、将现有文件截断为零长度或在文件不存在时创建该文件。
"r+"打开一个文本文件进行更新（即读取和写入）。"w+"打开一个文本文件进行更新（读取和写入），首先将文件截断为零长度（如果存在）或如果文件不存在则创建文件。
I mean the difference is that if I open the file with "w+", the file will be erased first?
我的意思是不同的是，如果我用 来打开文件"w+"，文件会先被删除？
采纳答案by haccks
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.
主要区别是w+将文件截断为零长度（如果存在）或创建新文件（如果不存在）。虽然r+没有删除该内容，也没有创建一个新的文件，如果它不存在。
Try these codes and you will understand:
试试这些代码，你就会明白：
#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);
}
and then this
然后这个
#include <stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "w+");
fclose(fp);
}
Then open the file test.txtand 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.
然后打开文件test.txt，看看会发生什么。您将看到第一个程序写入的所有数据都已被擦除。
重复此操作r+并查看结果。希望你会明白。
回答by Peter
Both r+and w+can read and write to a file. However, r+doesn't delete the content of the file and doesn't create a new file if such file doesn't exist, whereas w+deletes the content of the file and creates it if it doesn't exist.
双方r+并w+可以读取和写入文件。但是，r+如果文件不存在，则不会删除文件的内容，也不会创建新文件，而如果文件不存在，则w+删除文件的内容并创建它。
回答by invalid_id
r = read mode only
r+ = read/write mode
w = write mode only
w+ = read/write mode, if the file already exists override it (empty it)
So yes, if the file already exists w+ will erase the file and give you an empty file.
所以是的，如果文件已经存在 w+ 将删除文件并给你一个空文件。
回答by Waqar Naeem
This diagram will be faster to read next time. Maybe someone else will find that helpful too. This is clearly explained the difference between. 
下次阅读此图会更快。也许其他人也会觉得这很有帮助。这清楚地解释了两者之间的区别。
回答by Sathvik
w+
w+
#include <stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "w+"); //write and read mode
fprintf(fp, "This is testing for fprintf...\n");
rewind(fp); //rewind () function moves file pointer position to the beginning of the file.
char ch;
while((ch=getc(fp))!=EOF)
putchar(ch);
fclose(fp);
}
output
输出
This is testing for fprintf...
test.txt
测试.txt
This is testing for fprintf...
wand rto form w+
w和r形成w+
#include <stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "w"); //only write mode
fprintf(fp, "This is testing for fprintf...\n");
fclose(fp);
fp = fopen("test.txt", "r");
char ch;
while((ch=getc(fp))!=EOF)
putchar(ch);
fclose(fp);
}
output
输出
This is testing for fprintf...
test.txt
测试.txt
This is testing for fprintf...
r+
r+
test.txt
测试.txt
This is testing for fprintf...
#include<stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "r+"); //read and write mode
char ch;
while((ch=getc(fp))!=EOF)
putchar(ch);
rewind(fp); //rewind () function moves file pointer position to the beginning of the file.
fprintf(fp, "This is testing for fprintf again...\n");
fclose(fp);
return 0;
}
output
输出
This is testing for fprintf...
test.txt
测试.txt
This is testing for fprintf again...
rand wto form r+
r和w形成r+
test.txt
测试.txt
This is testing for fprintf...
#include<stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "r");
char ch;
while((ch=getc(fp))!=EOF)
putchar(ch);
fclose(fp);
fp=fopen("test.txt","w");
fprintf(fp, "This is testing for fprintf again...\n");
fclose(fp);
return 0;
}
output
输出
This is testing for fprintf...
test.txt
测试.txt
This is testing for fprintf again...
a+
一个+
test.txt
测试.txt
This is testing for fprintf...
#include<stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "a+"); //append and read mode
char ch;
while((ch=getc(fp))!=EOF)
putchar(ch);
rewind(fp); //rewind () function moves file pointer position to the beginning of the file.
fprintf(fp, "This is testing for fprintf again...\n");
fclose(fp);
return 0;
}
output
输出
This is testing for fprintf...
test.txt
测试.txt
This is testing for fprintf...
This is testing for fprintf again...
aand rto form a+
a和r形成a+
test.txt
测试.txt
This is testing for fprintf...
#include<stdio.h>
int main()
{
FILE *fp;
fp = fopen("test.txt", "a"); //append and read mode
char ch;
while((ch=getc(fp))!=EOF)
putchar(ch);
fclose(fp);
fp=fopen("test.txt","r");
fprintf(fp, "This is testing for fprintf again...\n");
fclose(fp);
return 0;
}
output
输出
This is testing for fprintf...
test.txt
测试.txt
This is testing for fprintf...
This is testing for fprintf again...
回答by perreal
There are 2 differences, unlike r+, w+will:
有2个区别，不像r+，w+将：
- create the file if it does not already exist
- first truncate it, i.e., will delete its contents
- 如果文件不存在，则创建该文件
- 首先截断它，即会删除它的内容
回答by Ashwani Bansal
r+ The existing file is opened to the beginning for both reading and writing. w+ Same as w except both for reading and writing.
r+ 现有的文件被打开到开头进行读取和写入。w+ 与 w 相同，除了读和写。
