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读取A.JPG（28KB）并将其保存到数组memblock中。但是为什么memblock的大小是4而不是28403而变量大小等于28403？

谢谢。

Answer 1

因为memblock是一个指针，所以sizeof运算符的计算结果是指针变量的大小，即4个字节。

Answer 2

谢谢大家，最后我用了向量。因为似乎很难显示我想要的结果（实际char数组的长度）

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";

在c ++中将二进制文件读入char数组

2 个答案: