fread（）的问题总是返回1 [英] problems with fread() always returning 1

问题描述

我看过类似的问题，但是我的问题有所不同。我确保以二进制模式打开文件，并检查读取时是否发生错误。

I have looked at similar questions, but mine is a bit different. I make sure to open file in binary mode and to check if error occurs while reading.

文件内容：

message1, message2, 53467

程序可读取简单文件：

program to read simple file:

int bytesRead;
FILE* CSV;
CSV = fopen("\\Temp\\csv.txt", "rb");
char dataBuf[128];

while ( (bytesRead = fread(dataBuf, 1, sizeof(dataBuf), CSV) > 0) )
{
        if (ferror(CSV))
            //handle error

        //do stuff with dataBuf contents
}

fread（）始终返回1。也不输入错误，因此不会出现文件读取错误。但是，char数组dataBuf充满了文件中的整个消息。我将fread与另一个函数结合使用，因此我需要知道使用fread（）读取了多少字节。有什么想法吗？

fread() is always returning 1. ferror is also not entered, so no file reading error. However, the char array dataBuf is filled with the entire message from the file. I am using fread in conjunction with another function so I need to know how many bytes were read using fread(). Any ideas?

推荐答案

优先级很重要。

在作业周围添加括号。

Add parenthesis around assignment.

while  (  (  bytesRead = fread(dataBuf, 1, sizeof(dataBuf), CSV)  )  > 0  )   
          ^                                                       ^

请参见 C_Operator_Precedence_Table

如果您看到 1.5.1文件复制 C编程语言中的部分> Brian W. Kernighan和Dennis M. Ritchie 您将对此有清楚的解释。

If you see 1.5.1 File Copying section of The C programming Language By Brian W. Kernighan and Dennis M. Ritchie You will get clear explanation on This.

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