C++ gdb 中的算术异常，但我没有除以零？
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Arithmetic Exception in gdb, but I'm not dividing by zero?
提问by crognale
I've been getting a Floating point exception (core dumped)error in my C++ program, and gdb shows that the problem is on a line that performs modulo division:
我的Floating point exception (core dumped)C++ 程序出现错误，gdb 显示问题出在执行模除法的行上：
Program received signal SIGFPE, Arithmetic exception.
[Switching to Thread 0x7ffff6804700 (LWP 13931)]
0x00000000004023e8 in CompExp::eval (this=0x7fffec000e40, currVal=0)
at exp.cpp:55
55 return (r==0) ? 0 : l % r;
The line guards against dividing by zero, and my backtrace shows the following:
该行防止被零除，我的回溯显示如下：
#0 0x00000000004023e8 in CompExp::eval (this=0x7fffec000e40, currVal=0)
at exp.cpp:55
l = -2147483648
r = -1
Since I know I'm not dividing by zero, what else could possibly be causing the exception?
既然我知道我没有被零除，那么还有什么可能导致异常？
回答by crognale
So I figured out what was causing the problem -- An arithmetic exception can be triggered either by dividing by zero, or overflow of a signedinteger, which is what happened here. Unsigned integers are required to wrap around when overflowed; the behavior for signed integers is undefined.
所以我找出了导致问题的原因——算术异常可以通过除以零或有符号整数溢出来触发，这就是这里发生的情况。溢出时需要无符号整数环绕；有符号整数的行为未定义。
回答by PeterJ
Change the code to the following to avoid trying to take the modulo of a negative number which is undefined:
将代码更改为以下内容，以避免尝试对未定义的负数取模：
return (r<=0) ? 0 : l % r;
回答by DocKimbel
In order to calculate such modulo expression: -2147483648 % -1, a division is required, which in this case, seems to be a 32-bit division (I guess land rare defined as int). The right result of such division would be 2147483648, but that value cannot be represented in 32-bit, so an arithmetic exception is produced.
为了计算这样的模表达式：-2147483648 % -1，需要一个除法，在这种情况下，这似乎是一个 32 位除法（我猜l并且r被定义为int）。这种除法的正确结果是2147483648，但该值不能用 32 位表示，因此会产生算术异常。
