这里是一个完整的例子 - 编译和运行，将map的内容写入文件并在读取后立即读取：
#include <map>
#include <fstream>
#include <iostream>
using namespace std;
int main(int argc, char* argv[])
{
std::string fname("test.bin");
std::map<unsigned,unsigned> testMap;
testMap[0]=103;
testMap[1]=2;
testMap[5]=26;
testMap[22]=4;
std::ofstream output(fname.c_str(),std::ios_base::binary|std::ios_base::trunc);
for(std::map<unsigned,unsigned>::iterator iter = testMap.begin();iter != testMap.end();++iter)
{
unsigned temp = iter->first;
output.write((const char*)&temp,sizeof(temp));
unsigned temp1 = iter->second;
output.write((const char*)&temp1,sizeof(temp1));
std::cerr << temp <<" "<<temp1<<" "<<std::endl;
}
std::cerr << "wrote bytes.........."<<output.tellp()<<", map size "<<testMap.size()<<std::endl;
output.flush();
output.close();
std::ifstream input(fname.c_str());
// retrieve length of file:
input.seekg (0, input.end);
unsigned streamSize = input.tellg();
input.seekg (0, input.beg);
char* buff = new char[streamSize];
input.read(buff,streamSize);
cerr << "sizeof of input......"<<streamSize << endl;
cerr << "read bytes..........."<<input.gcount() << endl;
::getchar();
return 0;
}
它会产生以下输出：
0 103
1 2
5 26
22 4
wrote bytes..........32, map size 4
sizeof of input......32
read bytes...........20
问题在于读取的字节数与写入的字节数不匹配，如何读/写整个映射表。
附注：在线编译器给出了32个读取字节的预期输出，在使用Visual Studio 2010专业版编译时，我得到了错误的输出。