strcpy将随机数添加到空字符串(strcpy adding random numbers to empty string)

 我试图通过使用strcpy(buffer, "")来清除char缓冲区。 strcpy()似乎在字符串中放入随机数。 在gdb中，我看到缓冲区（ received_message ）： 
 
 在strcpy()调用之前： 
 
(gdb) print received_message
$6 = "9210070627\000\000\000\000\000\000\000\000\000"
 
 在strcpy()调用之后： 
 
(gdb) print received_message
$8 = "\000\062\061\060\060\067\060\066\062\067\000\000\000\000\000\000\000\000\000"
 
 其中\060 ... \067 = 48 ... 65。 
 
 我在代码中的strcpy()调用只是strcpy(received_message, ""); 所以我不确定发生了什么。 
 
 我已经解决了实际问题，只是放入一个空终止符，而不是试图使字符串为空，因为我知道字符串的长度，但我仍然很好奇这里发生了什么。 
 
 编辑：似乎有些人想要更多的背景知道为什么我这样做。 我这样做是因为我正在使用zmq，它发送和接收没有null终止符的字符串。 我在测试中遇到了一个问题，我在做以下事情： 
 
Send 1234
Receive 1234
Send 123
Receive 1234
Send 12345
Receive 12345
Send 1234
Receive 12345
 
 似乎正在发生的事情是我正在重用我的缓冲区来接收消息（ received_message ），如果前一个字符串长于正在接收的字符串，则保留值。 
 
 为了解决这个问题，我想“刷新”缓冲区，这意味着我想将它全部设置为空字符。 通过阅读其他一些答案，看起来strcpy(received_message, "")可以做到这一点， recived_message[0] = 0 。 但是，这些都不起作用，因为它们只将第一个字符设置为null。 我知道“刷新”缓冲区的memset()方法，但是读到它比strcpy(received_message, "")东西要慢一些，所以没有使用它。 我想出的解决方案（并在下面显示）避免使用memset()设置整个数组，所以我对它有点开心，尽管它可能完全没有任何区别。 
 
 令我感到困惑的是，这个strcpy()调用用前缀为\06的单个数字替换了字符串中原来的数字，我误认为是\060等ASCII字符而不是前缀为\06 0。 
 
 我已经修复了接收消息的问题，因为zmq_recv()返回没有空终止符的字符串长度，所以要在接收消息的末尾放置一个空字符，我们只需要做 
 
int received_length = zmq_recv(request_socket, received_message, 20, 0);
received_message[received_length] = 0;
 
 在这种情况下， received message是一个20元素的char数组，我担心收到比这种情况更长的消息。 
 
 解决问题之后，我仍然对我的strcpy()调用发生了什么感到好奇，尽管我没有正确理解发生了什么。 我仍然很好奇为什么这些数字都以\06为前缀。 

I am trying to flush out a char buffer by using strcpy(buffer, ""). strcpy() seems to be putting random numbers in the string. In gdb, I see the buffers (received_message):
 
Before strcpy() call:
 
(gdb) print received_message
$6 = "9210070627\000\000\000\000\000\000\000\000\000"
 
After strcpy() call:
 
(gdb) print received_message
$8 = "\000\062\061\060\060\067\060\066\062\067\000\000\000\000\000\000\000\000\000"
 
Where \060 ... \067 = 48 ... 65.
 
My strcpy() call in the code is simply strcpy(received_message, "");, so I am not sure what is going on.
 
I have solved the actual issue by just putting in a null terminator rather than trying to make the string empty since I know the length of the string, but I am still very curious about what is going on here.
 
EDIT: It seems that some people want some more background on why I am doing this. I was doing this as I am using zmq, which sends and received strings without the null terminator. I was running into a problem in a test where I was doing the following:
 
Send 1234
Receive 1234
Send 123
Receive 1234
Send 12345
Receive 12345
Send 1234
Receive 12345
 
What seemed to be happening is that I was reusing my buffer for receiving messages (received_message), which was retaining values if the previous string was longer than the one that was being received.
 
To fix this, I wanted to "flush" the buffer, meaning I wanted to set it all to null characters. From reading some other answers, it seemed that strcpy(received_message, "") would do the trick, as would recived_message[0] = 0. However, neither of these would work as they only set the first character to null. I knew of the memset() method of "flushing" the buffer, but read that it was a bit slower than something such as strcpy(received_message, ""), so did not use it. The solution I figured out (and show below) avoids setting the whole array with memset(), so I am a bit happier with it, although it likely makes no difference at all.
 
What confused me is the fact that this strcpy() call replaced what was originally a number in a string by the individual numbers prefixed with \06, which I has mistaken for ASCII characters such as \060 rather than 0 prefixed by \06.
 
I have fixed the issue with receiving the message since zmq_recv() returns the string length without the null terminator, so to put a null character at the end of the received message, we only need to do
 
int received_length = zmq_recv(request_socket, received_message, 20, 0);
received_message[received_length] = 0;
 
In this case, received message is a 20-element array of char and I'm worried about receiving messages longer than that in this case.
 
After solving the problem, I was still curious about what was going on with my strcpy() call, although I was not correctly understanding what was happening. I am still curious why the numbers were being prefixed with \06 though.

原文：https://stackoverflow.com/questions/30460241