Question

我的编程有问题，我完全不知道为什么我不能在程序中使用qsort以有序的方式对这些struct数组进行排序？可以用某种方式帮助我吗？在这个程序中，有4个节点，每个节点代表一个文件，节点有文件名，大小和文件类型。我想根据文件名对它进行排序，但我完全不知道为什么qsort根本不起作用！

#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <unistd.h>



//int cmp(const void *a,const void*b);



typedef struct  node
{
        char filename[255];
        char filetype[255];
        long ofilesize;
        long newfilesize;
}Node;
Node Line[4];

int cmp(const void *a,const void*b)
{

    return strcmp(((Node *)a)->filename,((Node *)b)->filename);
}

int main(){
  /*  int j=0;
    for(;j<4;j++){
       Line[j]=(Node*)malloc(sizeof(Node));

    }*/
    strcpy(Line[0].filename,"b.txt");
   strcpy(Line[1].filename,"c.txt");
    strcpy(Line[2].filename,"d.txt");
     strcpy(Line[3].filename,"e.txt");

    int i=0;
    for(;i<4;i++){
       strcpy(Line[i].filetype,"regular file");
       Line[i].ofilesize=i;
       Line[i].newfilesize=i;

    }    



    for(i=0;i<4;i++)
    {
printf("File %s has type %s original size %ld new size %ld \n",Line[i].filename,Line[i].filetype,Line[i].ofilesize,Line[i].newfilesize);

    }

     qsort((void *)&Line,4,sizeof(Node),cmp);


    for(i=0;i<4;i++)
    {
printf("File %s has type %s original size %ld new size %ld \n",Line[i].filename,Line[i].filetype,Line[i].ofilesize,Line[i].newfilesize);

    }


}

这是我的输出：

File b.txt has type regular file original size 0 new size 0 
File c.txt has type regular file original size 1 new size 1 
File d.txt has type regular file original size 2 new size 2 
File e.txt has type regular file original size 3 new size 3 
File b.txt has type regular file original size 0 new size 0 
File c.txt has type regular file original size 1 new size 1 
File d.txt has type regular file original size 2 new size 2 
File e.txt has type regular file original size 3 new size 3

Answer 1

被删除的评论作者所说的是

int cmp(Node *a,Node *b) {
    return strcmp(a->filename,b->filename);
}

应该是

int cmp(Node **a,Node **b) {
    return strcmp((*a)->filename,(*b)->filename);
}

如果你想保留你的指示。

Answer 2

使用C ++ 11很容易解决。让编译器为你处理内存分配，并避免所有那些讨厌的指针。

#include <array>
#include <string>
#include <algorithm>

struct Node
{
    std::string filename;
    std::string filetype;
    long ofilesize;
    long newfilesize;
};

bool CompareByFilename(const Node& lhs, const Node& rhs)
{
    return lhs.filename < rhs.filename;
}

int main()
{
    std::array<Node, 4> line;
    line[0].filename = "e.txt";
    line[1].filename = "d.txt";
    line[2].filename = "c.txt";
    line[3].filename = "b.txt";

    for (unsigned int i = 0; i < line.size(); i++)
    {
        line[i].filetype = "regular file";
        line[i].ofilesize = i;
        line[i].newfilesize = i;
    }

    std::sort(line.begin(), line.end(), CompareByFilename);
}

考虑使用枚举作为文件类型，您确定long总是足够大以容纳文件大小吗？

如何在C中使用qsort对struct数组进行排序？

2 个答案: