sizeof(Array) 是如何工作的 [英] How Does sizeof(Array) work

问题描述

c 如何在运行时找到数组的大小?关于数组大小或数组边界的信息存储在哪里?

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

sizeof(array) 完全由 C 编译器实现.当程序被链接时，对你的 sizeof() 调用已经被转换成一个常量.

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.

示例:当您编译此 C 代码时:

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));
}

你得到

    .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

中间的$132是数组的大小，132 = 4 * 33.注意这里没有call sizeof指令——不像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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