C / C ++，指针和函数的麻烦 [英] C/C++, troubles with pointers and functions

问题描述

我有一个关于理解指针和函数如何工作的小问题。
我想看看函数看起来像 qsort（），但我需要使用我自己的函数来交换元素和比较元素。我很惊讶地知道我的函数不会交换数据...

我的代码：

<$ p $ （char * pcFirst，int nNumber，int size，void（* Swap）（void *，void *）， int（* Compare）（void *，void *））; //排序任何数组
void SwapInt（void * p1，void * p2）; //交换指针
int CmpInt（void * p1，void * p2）; // compare poineters

//实现文件：other.cpp

#includeother.h
void排序（char * pcFirst，int nNumber，int大小，
void（* Swap）（void *，void *），int（* Compare）（void *，void *））
{
int i;
for（i = 1; i< nNumber; i ++）
for（int j = nNumber-1; j> = i; j--）
{
char * pCurrent = pcFirst + j * size;
char * pPrevious = pcFirst +（j - 1）* size; $（b * b）if（（* Compare）（pPrevious，pCurrent）> 0）// if>> 0然后交换
{
（* Swap）（pPrevious，pCurrent）;




void SwapInt（void * p1，void * p2）
{
int * ptmp1 = static_cast< int * GT;（P1）;
int * ptmp2 = static_cast< int *>（p2）;
int * ptmp = ptmp1;
ptmp1 = ptmp2;
ptmp2 = ptmp;
}

int CmpInt（void * p1，void * p2）
{
int nResult;
int * ptmp1 = static_cast< int *>（p1）;
int * ptmp2 = static_cast< int *>（p2）;
nResult =（* ptmp1 - * ptmp2）;
返回nResult;
}

//主文件：lab.cpp
#include< tchar.h>
#include< iostream>
#include< cstdio>
#include< cmath>
#includeother.h

int _tmain（）
{
int nAr [] = {33,44,55,22,11}; // array for sort
int nTotal = sizeof（nAr）/ sizeof（int）; //元素数量
（int i = 0; i< nTotal; i ++）
{
printf（％d，nAr [i]）; //结果周期为33 44 55 22 11

排序（reinterpret_cast< char *>（& nAr [0]），nTotal，sizeof（int），SwapInt，CmpInt）;
for（int i = 0; i< nTotal; i ++）
{
printf（％d，nAr [i]）; //循环的结果是33 44 55 22 11 too =（
）
}

为什么数组没有改变？

在调试器中，我可以看到所有的指针都改变了，并且得到了正确的值，但是在 main

您可以看看这些不同的组合...... 。

  #include< iostream> 
 #include< stdio.h> 
＃include< malloc。 h> 
 //由地址调用
 void SwapIntAddr（int * ptmp1，int * ptmp2）
 {
 int ptmp; 
 ptmp = * ptmp1; 
 * ptmp1 = * ptmp2; 
 * ptmp2 = ptmp; 
} 
 
 //调用引用
 
 void SwapIntRef（int& ptmp1，int& amp; ; ptmp2）
 {
 int ptmp; 
 ptmp = ptmp1; 
 ptmp1 = ptmp2; 
 ptmp2 = ptmp; 
} 
 //通过引用调用，但在指针级别
 void SwapPtrRef（int *& p tmp1，int *& ptmp2）
 {
 int * ptmp; 
 ptmp = ptmp1; 
 ptmp1 = ptmp2; 
 ptmp2 = ptmp; 
} 
 
 //按地址呼叫，但在指针级别。 
 
 void SwapPtrAddr（int ** ptmp1，int ** ptmp2）
 {
 int ** ptmp =（int **）malloc（sizeof（int *））; 
 * ptmp = * ptmp1; 
 * ptmp1 = * ptmp2; 
 * ptmp2 = * ptmp; 
} 
 
 
 int main（）{
 int a = 3，b = 5; 
 int * p1 =& a; 
 int * p2 =& b; 
 
 SwapIntAddr（p1，p2）; 
 printf（％d％d \\\
，* p1，* p2）; 
 
 SwapIntRef（* p1，* p2）; 
 printf（％d％d \\\
，* p1，* p2）; 
 
 SwapPtrRef（p1，p2）; 
 printf（％d％d \\\
，* p1，* p2）; 
 
 SwapPtrAddr（& p1，& p2）; 
 printf（％d％d \\\
，* p1，* p2）; 
 
返回0; 
} 
  

I have a little question about understand how pointers and functions work. I want to see how a function looks like qsort(), but I need to use my own function to swap elements and to compare elements. I am very surprised to know that my function does not swap data...

My code:

//prototypes file: other.h

void Sort(char* pcFirst, int nNumber, int size, void (*Swap)(void*, void*), int (*Compare)(void*, void*) ); //sorts any arrays
void SwapInt(void* p1, void* p2); // swap pointers
int CmpInt(void* p1, void* p2); // compare poineters 

//realisation file: other.cpp

#include "other.h"
void Sort(char* pcFirst, int nNumber, int size,
     void (*Swap)(void*, void*), int (*Compare)(void*, void*) )
{
    int i;
    for( i = 1; i < nNumber; i++)
        for(int j = nNumber - 1; j >= i; j--)
        {
            char* pCurrent = pcFirst + j * size;
            char* pPrevious = pcFirst + (j - 1) * size;
            if( (*Compare)( pPrevious, pCurrent ) > 0 )// if > 0 then Swap
            {
                (*Swap)( pPrevious, pCurrent );
            }
        }
}

void SwapInt(void* p1, void* p2) 
{
    int * ptmp1 = static_cast<int*>(p1);
    int * ptmp2 = static_cast<int*>(p2);
    int * ptmp = ptmp1;
    ptmp1 = ptmp2;
    ptmp2 = ptmp;
}

int CmpInt(void* p1, void* p2)
{
    int nResult;
    int * ptmp1 = static_cast<int*>(p1);
    int * ptmp2 = static_cast<int*>(p2);
    nResult = (*ptmp1 - *ptmp2);
    return nResult;
}

//main file: lab.cpp
#include <tchar.h>
#include <iostream>
#include <cstdio>
#include <cmath>
#include "other.h"

int _tmain()
{
int nAr[] = {33,44,55,22,11};   //array for sort
    int nTotal = sizeof(nAr) / sizeof(int); //number of elements
for ( int i = 0; i < nTotal; i++)
    {
        printf("%d ",nAr[i]); // result of cycle is 33 44 55 22 11
    }
    Sort(reinterpret_cast<char*>(&nAr[0]), nTotal, sizeof(int), SwapInt, CmpInt);
for ( int i = 0; i < nTotal; i++)
    {
        printf("%d ",nAr[i]); // result of cycle is 33 44 55 22 11 too =(
    }
}

Why does the array not change?

In the debugger I can see that all pointers change, and get correct values, but in main my array is not changed.

解决方案

You may look at various combinations as these.....

#include<iostream>
#include<stdio.h>
#include<malloc.h>
//Call by Address
    void SwapIntAddr(int* ptmp1, int* ptmp2) 
    {
        int ptmp;
        ptmp  = *ptmp1;
        *ptmp1 = *ptmp2;
        *ptmp2 = ptmp;
    }

//Call by Reference

    void SwapIntRef(int& ptmp1, int& ptmp2) 
    {
         int ptmp;
         ptmp  = ptmp1;
         ptmp1 = ptmp2;
         ptmp2 = ptmp;
    }
//Call by Reference but in pointer level
    void SwapPtrRef(int*& ptmp1, int*& ptmp2) 
    {
         int* ptmp;
         ptmp  = ptmp1;
         ptmp1 = ptmp2;
         ptmp2 = ptmp;
    }

//Call by Address but in Pointer level.

    void SwapPtrAddr(int** ptmp1,int** ptmp2) 
    {
        int** ptmp = (int**) malloc(sizeof(int*));
        *ptmp  = *ptmp1;
        *ptmp1 = *ptmp2;
        *ptmp2 = *ptmp;
    }


int main(){
  int a = 3, b= 5;
  int* p1 = &a;
  int* p2 = &b;

  SwapIntAddr(p1,p2);
  printf("%d %d\n",*p1,*p2);

  SwapIntRef(*p1,*p2);
  printf("%d %d\n",*p1,*p2);

  SwapPtrRef(p1,p2);
  printf("%d %d\n",*p1,*p2);

  SwapPtrAddr(&p1,&p2);
  printf("%d %d\n",*p1,*p2);

  return 0;
}

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