小编ada*_*hie的帖子

我正在尝试运行程序,在Ubuntu 12.10上使用boost :: filesystem的示例代码,但它不想构建.

#include <iostream>
#include <boost/filesystem.hpp>
using namespace boost::filesystem;
using namespace std;

void fun(const string& dirPath);
int main()
{
    fun("/home");
    return 0;
}

void fun(const string& dirPath)
{
    path p (dirPath); 

    if (exists(p))  
    {
        if (is_regular_file(p))   
            cout << p << " size is " << file_size(p) << '\n';

        else if (is_directory(p))    
            cout << p << "is a directory\n";

        else
            cout << p << "exists, but is neither a regular file nor a directory\n";
    }
    else
        cout << p …

我得到了结构:

typedef struct
{
    int a;
    int b;
    int c;
}Z;

码:

int main()
{
    Z *a = (Z*)malloc(sizeof(Z)*8);
    Z *b = (Z*)malloc(sizeof(Z)*8);
    printf("%lu\n", sizeof(Z));
    printf("%p %p\n", b, a);
    printf("%lu\n", b - a);
}

输出:

12
0x89a080 0x89a010
12297829382473034420

为什么最后一行的价值如此之大？实际地址差异是0x70(16个字节的堆分配头加上数组a的12*8个字节的元素),所以从指针的算术我期望值0x70/12 = 9.(3)或9转换为整数.我知道减去指针不指向相同的数组,但我期望更合理的结果,这将让我知道内存映射的样子.它是在64b Ubuntu和gcc 4.8.2上编译的.

部件:

    .file   "aa.c"
    .section    .rodata
.LC0:
    .string "%lu\n"
.LC1:
    .string "%p %p\n"
    .text
    .globl  main
    .type   main, @function
main:
.LFB2:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    subq    $16, %rsp …