在C++中將二進制文件讀入字符數組中

Question

std::streampos size; 
char * memblock; 

std::ifstream input ("A.JPG", std::ios::in|std::ios::binary|std::ios::ate); 

if (input.is_open()) 
{ 
    size = input.tellg(); 
    memblock = new char [size]; 
    input.seekg (0, std::ios::beg); 
    input.read (memblock, size); 
    input.close(); 

    std::cout << "[INPUT]the entire file content is in memory " << sizeof(memblock) << " \n"; 

} 
delete[] memblock; 

我想使用ifstream來讀取A.JPG（28KB）並將其保存到數組memblock中。但爲什麼memblock的大小是4而不是28403而變量大小等於28403？

謝謝。

Answer 1

因爲memblock是一個指針，所以sizeof運算符評估指針變量的大小，即4個字節。

Answer 2

感謝所有，最後我用了矢量。 因爲似乎很難顯示結果我想要（實際字符數組的長度）

std::vector <char> memblock(0); 
    if (input.is_open()) 
    { 
    size = input.tellg(); 
    //memblock = new char [size]; 
    memblock.resize(size); 
    input.seekg (0, std::ios::beg); 
    input.read (&memblock[0], size); 
    input.close(); 


    //std::cout << "[INPUT]the entire file content is in memory " << ((char *)(&memblock+1) - (char *)memblock)/(sizeof(memblock[0])) << " \n"; 
    std::cout << "[INPUT]the entire file content is in memory " << memblock.size() << " \n";