c++castingx86movsign-extension

A compilation problems in VS2015

   127:    int a = 2815;
00007FF78B5126EE  mov dword ptr [a],0AFFh
   128:
   129:    short c = static_cast<char>(a);
00007FF78B5126F5  movsx    ax,byte ptr [a]
00007FF78B5126FA  mov      word ptr [c],ax

In my environment an int takes 4 byte and a short takes 2, so in the movsx instruction, why there is a byte not a word? Hope someone can help me!

Solution

  • A char is one byte. The static_cast casts a to a char. One byte. Hence, the one-byte value of the char-cast variable a is moved into ax.