需要帮助理解C中的指针

问题描述

我实际上非常理解指针，我只是在下面发布的代码中的一件事情上感到困惑。不仅是指针而是写（unsigned int），然后是变量名或函数。代码如下，我评论了我需要解释的内容，这是我从教科书中得到的代码。

I actually understand pointers very well, I am just confused mostly on one thing in the code i posted below. Not only pointers but writing (unsigned int) then a variable name or function after it. The code is below, I commented what i need explaining, this is code I am getting from a text book.

#include <stdio.h>
#include <ctype.h>

typedef unsigned char BYTE;

int main(void)
{
    unsigned int addr;
    int i , n;
    BYTE* ptr;

    printf("Address of main function: %x\n" , (unsigned int) main); //why is unsigned int here?
    printf("Address of addr variable: %x\n" , (unsigned int) &addr);//and here also?

    printf("\nEnter a (hex) address: ");
scanf("%x" , &addr);
    printf("Enter Number of bytes to view: ");
scanf("%d" , &n);

    printf("\n");
    printf("Address                 Bytes               Characters\n");
    printf("-------               --------              -----------");

ptr = (BYTE*)addr;//is ptr a conversion from int to BYTE*? I do not understand this.This is what i need explaining most with

for(; n > 0;n -= 10)
{
    printf("%8X   " , (unsigned int) ptr); //what does unsigned int mean in front of ptr and why is it needed?
    for(i = 0; i < 10 && i < n; i++)
        printf("%.2X ", *(ptr + i));
    for(; i < 10; i++)
        printf("   ");
        printf("   ");
        for(i = 0; i <10 && i < n ; i++)
        {
            BYTE ch = *(ptr + i);
            if(!isprint(ch))
                ch ='.';
        printf("%c" , ch);
        }
        printf("\n");
        ptr += 10;
}
return 0;
}

推荐答案

#include <stdio.h>
#include <ctype.h>

typedef unsigned char BYTE;

int main(void)
{
    unsigned int addr;
    int i , n=50;
    BYTE* ptr;

    printf("Address of main function: %x\n" , (unsigned int) main); // unsigned int because we wish to print the adddress of main as an unsigned int
    printf("Address of addr variable: %x\n" , (unsigned int) &addr);// unsigned int because we wish to print the adddress of addr as an unsigned int

//    printf("\nEnter a (hex) address: ");
//scanf("%x" , &addr);
//    printf("Enter Number of bytes to view: ");
//scanf("%d" , &n);

	addr = (unsigned int) main; // Take the address of main

    printf("\n");
    printf("Address                 Bytes               Characters\n");
    printf("-------               --------              -----------\n");

ptr = (BYTE*)addr; // Assign addr to pointer. To do this we need to make a BYTE * pointer out of addr using a cast.
for(; n > 0; n -= 10)
{
    printf("%8X   " , (unsigned int) ptr); // ptr is a BYTE * and we wish to print its value as an unsigned int (the address)
    for(i = 0; i < 10 && i < n; i++)
        printf("%.2X ", *(ptr + i));
    for(; i < 10; i++)
        printf("   ");
        printf("   ");
        for(i = 0; i <10 && i < n ; i++)
        {
            BYTE ch = *(ptr + i);
            if(!isprint(ch))
                ch ='.';
        printf("%c" , ch);
        }
        printf("\n");
        ptr += 10;
}
return 0;
}

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