我正在嘗試為我的計算機機器組織類撰寫一個 C 程式，在該類中，我對存盤在記憶體中的某個地址執行十六進制的記憶體轉儲。我真的不明白什么是記憶體轉儲，并且對撰寫 C 很陌生。我的問題是：
- 如何創建一個采用兩個引數的方法，它們在記憶體中指定地址？
- 如何進一步修改這些引數以指定正好 4 個位元組長的字地址？
- 然后如何將這些地址轉換為十六進制值？
我知道這很多，但感謝您的任何建議。
對于任何需要它的人，這是我到目前為止的代碼：
#include <stdio.h>
// Create something to do the methods on
char array[3] = {'a', 'b', 'c'};
void mdump(char start, char end){
// Create pointers to get the address of the starting and ending characters
char* pointer1 = (char *)& start;
char* pointer2 = (char *)& end;
// Check to see if starting pointer is in lower memory than ending pointer
if(pointer1 < pointer2){
printf("Passed");
}
else{
printf("Failed");
}
// Modify both the arguments so that each of them are exactly 4 bytes
// Create a header for the dump
// Iterate through the addresses, from start pointer to end pointer, and produce lines of hex values
// Declare a struct to format the values
// Add code that creates printable ASCII characters for each memory location (print "cntrl-xx" for values 0-31, or map them into a blank)
// Print the values in decimal and in ASCII form
}
int main(){
mdump(array[0], array[2]);
return 0;
}
uj5u.com熱心網友回復：
如何在學習 C 的同時撰寫 Hex 轉儲工具：
- 從簡單的事情開始：
#include <iostream>
int main()
{
char test[32] = "My sample data";
// output character
std::cout << test[0] << '\n';
}
輸出：
M
在 coliru 上進行現場演示
- 列印十六進制值而不是字符：
#include <iostream>
int main()
{
char test[32] = "My sample data";
// output a character as hex-code
std::cout << std::hex << test[0] << '\n'; // Uh oh -> still a character
std::cout << std::hex << (unsigned)(unsigned char)test[0] << '\n';
}
輸出：
M
4d
在 coliru 上進行現場演示
筆記：
流輸出運算子 forchar旨在列印一個字符（當然）。還有另一個unsigned更適合的流輸出運算子。為了實作它的使用，char必須將其轉換為unsigned.
但要做好準備：C 標準并沒有規定是char有符號還是無符號——這個決定留給編譯器供應商。為了安全起見，'char' 首先轉換為 'unsigned char' 然后轉換為unsigned.
- Print the address of the variable with the character:
#include <iostream>
int main()
{
char test[32] = "My sample data";
// output an address
std::cout << &test[0] << '\n'; // Uh oh -> wrong output stream operator
std::cout << (const void*)&test[0] << '\n';
}
Output:
My sample data
0x7ffd3baf9b70
Live demo on coliru
Note:
There is one stream output operator for const char* which is intended to print a (zero-terminated) string. This is not what is intended. Hence, the (ugly) trick with the cast to const void* is necessary which triggers another stream output operator which fits better.
- What if the data is not a 2 digit hex?
#include <iomanip>
#include <iostream>
int main()
{
// output character as 2 digit hex-code
std::cout << (unsigned)(unsigned char)'\x6' << '\n'; // Uh oh -> output not with two digits
std::cout << std::hex << std::setw(2) << std::setfill('0')
<< (unsigned)(unsigned char)'\x6' << '\n';
}
Output:
6
06
Live demo on coliru
Note:
There are I/O manipulators which can be used to modify the formatting of (some) stream output operators.
- Now, put it all together (in loops) et voilà: a hex-dump.
#include <iomanip>
#include <iostream>
int main()
{
char test[32] = "My sample data";
// output an address
std::cout << (const void*)&test[0] << ':';
// output the contents
for (char c : test) {
std::cout << ' '
<< std::hex << std::setw(2) << std::setfill('0')
<< (unsigned)(unsigned char)c;
}
std::cout << '\n';
}
Output:
0x7ffd345d9820: 4d 79 20 73 61 6d 70 6c 65 20 64 61 74 61 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Live demo on coliru
- Make it nice:
#include <algorithm>
#include <iomanip>
#include <iostream>
int main()
{
char test[32] = "My sample data";
// hex dump
const size_t len = sizeof test;
for (size_t i = 0; i < len; i = 16) {
// output an address
std::cout << (const void*)&test[i] << ':';
// output the contents
for (size_t j = 0, n = std::min<size_t>(len - i, 16); j < n; j) {
std::cout << ' '
<< std::hex << std::setw(2) << std::setfill('0')
<< (unsigned)(unsigned char)test[i j];
}
std::cout << '\n';
}
}
Output:
0x7fffd341f2b0: 4d 79 20 73 61 6d 70 6c 65 20 64 61 74 61 00 00
0x7fffd341f2c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Live demo on coliru
- Make it a function:
#include <algorithm>
#include <iomanip>
#include <iostream>
void hexdump(const char* data, size_t len)
{
// hex dump
for (size_t i = 0; i < len; i = 16) {
// output an address
std::cout << (const void*)&data[i] << ':';
// output the contents
for (size_t j = 0, n = std::min<size_t>(len - i, 16); j < n; j) {
std::cout << ' '
<< std::hex << std::setw(2) << std::setfill('0')
<< (unsigned)(unsigned char)data[i j];
}
std::cout << '\n';
}
}
int main()
{
char test[32] = "My sample data";
std::cout << "dump test:\n";
hexdump(test, sizeof test);
std::cout << "dump 4 bytes of test:\n";
hexdump(test, 4);
std::cout << "dump an int:\n";
int n = 123;
hexdump((const char*)&n, sizeof n);
}
Output:
dump test:
0x7ffe900f4ea0: 4d 79 20 73 61 6d 70 6c 65 20 64 61 74 61 00 00
0x7ffe900f4eb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
dump 4 bytes of test:
0x7ffe900f4ea0: 4d 79 20 73
dump an int:
0x7ffe900f4e9c: 7b 00 00 00
Live demo on coliru
Note:
(const char*)&n may look a bit adventurous. In fact, conversion of pointers is always something which should be at best not necessary. However, for the dump tool this is the easiest way to access the bytes of arbitrary data. (This is one of the rare cases which is explicitly allowed by the standard.)
An even nicer hexdump can be found in
SO: How would I create a hex dump utility in C ?
(which I recommended OP beforehand).
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