如何更改firebird3中的列类型(How change a column type in firebird3)

 目前还不清楚你打算做什么，但代码完全按照你的要求去做。 
 
 AC“string”是一系列以null值结尾的char元素。 无论什么后面的空值不是字符串的一部分。 
 
 通话前的字符串： 
 
 
 
 “9210070627”（后跟一个空值，以及一系列可能属于缓冲区或调试器工件的空值，我们不知道）。 
 
 
 你的来电： 
 
 
 
 strcpy(buffer, "") （将空字符串复制到缓冲区，并以null值终止） 
 
 
 通话后你的字符串： 
 
 
 
 “” - 一个空字符串，后跟终止空值（加上“210070627”和前一个内容中剩余的空值作为工件，如上所述，这些工件不属于字符串的一部分）。 
 
 
 因此，您的缓冲区现在包含一个空字符串，如您所指示的那样。 它还包含原始数据的剩余部分，但buffer 确实指向空字符串。 strlen( buffer ) == 0 。 
 
 如果您打算擦除缓冲区的内容，即将整个缓冲区memset() ，则应尝试memset() 。 

It is unclear what you intended to do, but the code does exactly what you told it to do.
 
A C "string" is a series of char elements that ends with a null value. Whatever comes after that null value is not part of the string.
 
Your string before the call:
 
 
 
"9210070627" (followed by a null value, and a series of null values that might be part of the buffer or an artifact of the debugger, we don't know).
 
 
Your call:
 
 
 
strcpy(buffer, "") (copy empty string into buffer, and terminate with null value)
 
 
Your string after the call:
 
 
 
"" -- an empty string, followed by the terminating null value (plus the "210070627" and null values remaining from the previous content as artifacts which aren't part of the string as mentioned above).
 
 
So, your buffer now contains an empty string, as you instructed. It also contains remains of the original data, but buffer does point to an empty string. strlen( buffer ) == 0.
 
If you are intending to erase the contents of the buffer, i.e. zero-out the whole buffer, you should try memset().