fopen()中r +和w +之间的差异

Question

在fopen("myfile", "r+")什么之间的区别"r+"和"w+"开放模式？我看了这个:

"r" 打开文本文件进行阅读.
"w"打开文本文件以进行写入,将现有文件截断为零长度,或者创建文件(如果该文件不存在).

"r+"打开文本文件进行更新(即读取和写入).
"w+"打开文本文件以进行更新(读取和写入),首先将文件截断为零长度(如果存在)或创建文件(如果文件不存在).

我的意思是不同的是,如果我打开文件"w+",文件将被删除？

Answer 1

双方r+并w+可以读取和写入文件.但是,r+如果此类文件不存在,则不会删除文件的内容并且不会创建新文件,而w+删除文件的内容并在文件不存在时创建它.

Answer 2

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。

Answer 3

试试这些代码,您就会明白:

#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);
}  

然后这个

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

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

然后打开文件w+,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删除.
重复此操作r+并查看结果.希望你能理解.

Answer 4

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)

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.

Answer 5

瓦+

#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);
}  

输出

This is testing for fprintf...

测试.txt

This is testing for fprintf...

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);
}  

输出

This is testing for fprintf...

测试.txt

This is testing for fprintf...

r+

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;
}

输出

This is testing for fprintf...

测试.txt

This is testing for fprintf again...

r和w形成r+

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;
}

输出

This is testing for fprintf...

测试.txt

This is testing for fprintf again...

一个+

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;
}

输出

This is testing for fprintf...

测试.txt

This is testing for fprintf...
This is testing for fprintf again...

a和r形成a+

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;
}

输出

This is testing for fprintf...

测试.txt

This is testing for fprintf...
This is testing for fprintf again...