[英]Different behaviors between GCC and Clang
碼:
#include <cstdio>
int main() {
unsigned char a = -300.f;
printf("%d\n", a);
}
GCC編譯:
g++ test.cpp -o test -std=c++11
test.cpp: In function ‘int main()’:
test.cpp:4:21: warning: overflow in implicit constant conversion [-Woverflow]
unsigned char a = -300.f;
^
GCC結果:
0
GCC版本:
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.5) 5.4.0 20160609
lang編譯
clang++ test.cpp -o test -std=c++11
test.cpp:4:21: warning: implicit conversion from 'float' to 'unsigned char' changes value from 300 to 255
[-Wliteral-conversion]
unsigned char a = -300.f;
~ ^~~~~
1 warning generated.
鐺結果:
160
lang版本:
clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
也許標准沒有定義這種行為。
添加-fsanitize=undefined
:
GCC結果(相同):
0
lang結果(48 !?):
test.cpp:4:20: runtime error: value -300 is outside the range of representable values of type 'unsigned char'
48
將浮點類型轉換為unsigned char
其中浮點值超出unsigned char
的范圍)的行為是不確定的 。
請注意,這與原始類型是較寬的整數類型的情況不同。
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