如何做的sizeof（阵列）工作 [英] How Does sizeof(Array) work

问题描述

如何Ç发现在运行时数组的大小？其中存储了关于数组大小或数组的边界的信息？

How does c find at run time the size of array? where is the information about array size or bounds of array stored ?

推荐答案

的sizeof（阵列）完全是由C编译器实现的。该方案被链接的时候，看起来像一个的sizeof（）呼叫您已被改造成一个常数。

sizeof(array) is implemented entirely by the C compiler. By the time the program gets linked, what looks like a sizeof() call to you has been converted into a constant.

例如：当您编译此C code：

Example: when you compile this C code:

#include <stdlib.h>
#include <stdio.h>
int main(int argc, char** argv) {
    int a[33];
    printf("%d\n", sizeof(a));
}

你

    .file   "sz.c"
    .section        .rodata
.LC0:
    .string "%d\n"
    .text
.globl main
    .type   main, @function
main:
    leal    4(%esp), %ecx
    andl    $-16, %esp
    pushl   -4(%ecx)
    pushl   %ebp
    movl    %esp, %ebp
    pushl   %ecx
    subl    $164, %esp
    movl    $132, 4(%esp)
    movl    $.LC0, (%esp)
    call    printf
    addl    $164, %esp
    popl    %ecx
    popl    %ebp
    leal    -4(%ecx), %esp
    ret
    .size   main, .-main
    .ident  "GCC: (GNU) 4.1.2 (Gentoo 4.1.2 p1.1)"
    .section        .note.GNU-stack,"",@progbits

的 $ 132 中间是数组的大小，132 = 4 * 33，注意有没有呼叫的sizeof 指令 - 不像的printf ，这是一个真正的函数

The $132 in the middle is the size of the array, 132 = 4 * 33. Notice that there's no call sizeof instruction - unlike printf, which is a real function.

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