將無符號字符的向量寫入二進制文件C ++

Question

我正在將二進制文件cmd.exe讀入無符號字符數組。 讀入bytes_read的總字節數為153。我將其轉換為base64字符串，然后將該字符串解碼回（來自c ++中第二個答案base64解碼代碼段的代碼 ）到vector <'BYTE>中。 BYTE是未簽名的字符。 encodedData.size（）也是153。但是，當我以二進制模式將此向量寫入文件以再次獲取cmd.exe文件時，我僅得到1 KB文件。 我錯過了什么？

// Reading size of file
    FILE * file = fopen("cmd.exe", "r+");
    if (file == NULL) return 1;
    fseek(file, 0, SEEK_END);
    long int size = ftell(file);
    fclose(file);
// Reading data to array of unsigned chars
    file = fopen("cmd.exe", "r+");
    unsigned char * myData = (unsigned char *)malloc(size);
    int bytes_read = fread(myData, sizeof(unsigned char), size, file);
    fclose(file);

    std::string encodedData = base64_encode(&myData[0], bytes_read);
    std::vector<BYTE> decodedData = base64_decode(encodedData);

////write data to file
    ofstream outfile("cmd.exe", ios::out | ios::binary);
    outfile.write((const char *)decodedData.data(), decodedData.size());

更新：感謝@chux建議“ r +”->“ rb +”問題已解決。

Answer 1

您將其標記為C ++。

這是一種使用fstream讀取二進制文件的C ++方法。 為了簡化此示例，我創建了一個比所需的更大的m_buff。 從注釋中，聽起來您的fopen（“ cmd.exe”，“ r +”）錯誤，所以我僅提供C ++二進制讀取。

方法tReader（）a）以二進制模式打開文件，b）將數據讀入m_buff，並且c）捕獲gCount進行顯示。

它還演示了使用計時來測量持續時間的一種可能。

#include <chrono>
// 'compressed' chrono access --------------vvvvvvv
typedef std::chrono::high_resolution_clock  HRClk_t; 
typedef HRClk_t::time_point                 Time_t;  
typedef std::chrono::microseconds           US_t;    
using   namespace std::chrono_literals;  // suffixes 100ms, 2s, 30us

#include <iostream>
#include <fstream>
#include <cassert>

class T516_t
{
   enum BuffConstraints : uint32_t {
      Meg           = (1024 * 1024),
      END_BuffConstraints
   };

   char*   m_buff;
   int64_t m_gCount;

public:

   T516_t()
      : m_buff (nullptr)
      , m_gCount (0)
      {
         m_buff = new char[Meg];
      }

   ~T516_t() = default;

   int exec()
      {
         tReader();
         return(0);
      }

private: // methods

   void tReader()
      {
         std::string pfn = "/home/dmoen/.wine/drive_c/windows/system32/cmd.exe";
         // open file in binary mode
         std::ifstream sIn (pfn, std::ios_base::binary);

         if (!sIn.is_open()) {
            std::cerr << "UNREACHABLE:  unable to open sIn " << pfn
                      << " priviledges? media offline?";
            return;
         }

         Time_t start_us = HRClk_t::now();
         do
         {
            // perform read
            sIn.read (m_buff, Meg);
            // If the input sequence runs out of characters to extract (i.e., the
            // end-of-file is reached) before n characters have been successfully
            // read, buff contains all the characters read until that point, and
            // both eofbit and failbit flags are set

            m_gCount = sIn.gcount();

            if(sIn.eof()) { break; } // exit when no more data

            if(sIn.failbit ) {
               std::cerr << "sIn.faileBit() set" << std::endl;
            }

         }while(1);
         auto  duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);

         sIn.close();

         std::cout << "\n  " << pfn
                   << "   " << m_gCount << " bytes"
                   << "   " << duration_us.count() << " us"
                   << std::endl;

      } // int64_t tReader()

}; // class T516_t

int main(int , char**)
{
   Time_t start_us = HRClk_t::now();

   int retVal = -1;
   {
      T516_t   t516;
      retVal = t516.exec();
   }
   auto  duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);

   std::cout << "  FINI   " << duration_us.count() << " us" << std::endl;
   return(retVal);
}

我系統上的一個典型輸出如下所示：

/home/dmoen/.wine/drive_c/windows/system32/cmd.exe   722260 bytes  1180 us   
FINI   1417 us

您的結果會有所不同。

您的流使用看起來不錯（因此沒有重復）。