x86 程序集中的操作数大小冲突

问题描述

我刚刚开始为我的计算机组织课程在汇编中编程，每当我尝试在一个C程序.

I've just started programming in Assembly for my computer organization course, and I keep getting an operand size conflict error whenever I try to compile this asm block within a C program.

arrayOfLetters[] 对象是一个字符数组，所以每个元素不应该是一个字节吗?当我执行 mov eax, arrayOfLetters[1] 时，代码有效，但我不确定为什么会这样，因为 eax 寄存器是 4 个字节.

The arrayOfLetters[] object is a char array, so shouldn't each element be one byte? The code works when I do mov eax, arrayOfLetters[1], but I'm not sure why that works, as the eax register is 4 bytes.

#include <stdio.h>
#define SIZE 3

char findMinLetter( char arrayOfLetters[], int arraySize )
{
    char min;

    __asm{
        push eax
        push ebx
        push ecx
        push edx
        mov dl, 0x7f        // initialize DL

        mov al, arrayOfLetters[1] //Problem occurs here

        mov min, dl        // read DL
        pop edx
        pop ecx
        pop ebx
        pop eax
    }

    return min;
}

int main()
{
    char arrayOfLetters[ SIZE ] = {'a','B','c'};

    int i;

    printf("\nThe original array of letters is:\n\n");
    for(i=0; i<SIZE; i++){
        printf("%c ", arrayOfLetters[i]);
    }
    printf("\n\n");

    printf("The smallest (potentially capitalized) letter is: %c\n", findMinLetter( arrayOfLetters, SIZE ));

    return 0;
}

推荐答案

使用 mov al, BYTE PTR arrayOfLetters[1].

您可以使用 cl input.c/Faoutput.asm 使用 MSVC 编译代码以获得汇编打印输出 - 这将表明只需使用 arrayOfLetters[1]到 DWORD PTR 并且你需要明确说明你想要一个 BYTE PTR.

You can compile the code with MSVC using cl input.c /Faoutput.asm to get an assembly printout - this would show that simply using arrayOfLetters[1] translates to DWORD PTR and you need to explicity state you want a BYTE PTR.

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