C - fwrite() 不输出到文件

发布于 2024-10-06 08:42:04 字数 704 浏览 0 评论 0原文

从未使用过 fwrite()，所以我不确定我到底做错了什么。我现在只是测试它，我想做的就是尝试将单个字符写入文件，直到它到达末尾。我正在写入的文件是我从老师的网站下载的。当我检查它的属性时，类型仅列为“文件”。它应该只是一个 2MB 的空文件，供我们写入代码（如果有人想知道，请使用文件系统实验室）。这是我的代码：

#include <stdio.h>
#include <string.h>
int main()
{
    char c;
    FILE *fp;   
    char testing[2] = {'c'};  

    fp = fopen("Drive2MB", "rw"); 

    fseek(fp, 0, SEEK_SET);     //make sure pointers at beginning of file
    while((c=fgetc(fp))!=EOF)
    {
        fwrite(testing, 1, sizeof(testing), fp);
        fseek(fp, 1, SEEK_CUR);  //increment pointer 1 byte
    }
    fclose(fp);
}

当我运行此代码时，会弹出一条错误消息，显示“调试断言失败！...表达式：（“无效的文件打开模式”，0）并打印“程序'[3896] filesystem.exe：本机'已退出，代码为 3 (0x3)。”

原文

Never used fwrite(), so I'm not sure exactly what I'm doing wrong. I'm just testing it now and all I want to do is try to write a single char out to a file until it reaches the end. The file I'm writing to is one I downloaded from my teacher's website. When I check the properties of it, the type is only listed as "file". It's supposed to just be an empty 2MB file for us to write our code to (file system lab if anyone's wondering). Here's my code:

#include <stdio.h>
#include <string.h>
int main()
{
    char c;
    FILE *fp;   
    char testing[2] = {'c'};  

    fp = fopen("Drive2MB", "rw"); 

    fseek(fp, 0, SEEK_SET);     //make sure pointers at beginning of file
    while((c=fgetc(fp))!=EOF)
    {
        fwrite(testing, 1, sizeof(testing), fp);
        fseek(fp, 1, SEEK_CUR);  //increment pointer 1 byte
    }
    fclose(fp);
}

When I run this, an error message pops up saying "Debug Assertion Failed!...Expression:("Invalid file open mode",0) and prints "The program '[3896] filesystem.exe: Native' has exited with code 3 (0x3)."

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忱杏 2024-10-13 08:42:04

您已打开文件进行读取（这就是 fopen("Drive2MB", "r"); 中 r 的含义）。您不能写入为读取而打开的文件。

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清风疏影 2024-10-13 08:42:04

您正在以只读模式打开它

使用 r+ 作为 fopen

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雨后咖啡店 2024-10-13 08:42:04

fp = fopen("Drive2MB", "r")

您以只读方式打开文件

尝试

fp = fopen("Drive2MB", "r+");

fp = fopen("Drive2MB", "r")

your openning your file in read only

try

fp = fopen("Drive2MB", "r+");

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雪花飘飘的天空 2024-10-13 08:42:04

您已使用 fopen 的“r”部分打开文件进行读取。要写入文件，您可以以读/写模式或写入模式打开它。

// Read/write mode
fp = fopen("Drive2MB", "r+");

// Write only mode
fp = fopen("Drive2MB", "w");

我个人从来不喜欢使用“rw”。当您打开一个文件时，它确实应该有一个被打开的原因。您也不需要调用 fseek 来移动到文件的开头，也不需要使用 fseek 来前进文件指针。 fopen 会自动将其打开到文件的开头，而 fwrite 会自动前进指针。仅当您在文件内部“查找”以到达特定点时才应使用 fseek。

在您给出的情况下，您只需要写入（“w”）模式，因为您从未从文件中读取。

You've opened the file for reading with the "r" part of fopen. To write to the file, you can open it in read/write mode or write mode.

// Read/write mode
fp = fopen("Drive2MB", "r+");

// Write only mode
fp = fopen("Drive2MB", "w");

I never like to use "rw" personally. When you open a file, it really should have one reason to be opened. You also do not need to call fseek to move to the start of the file and you do not need to use fseek to advance the file pointer. fopen will automatically open it to the start of the file and fwrite will automatically advance the pointer. fseek should only be used if you are "seek"ing inside of the file to get to a specific point.

In the case you've given, you would only need write ("w") mode since you are not ever reading from the file.

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