c++ - How do I read a double from file? -

i came following code:

#include <stdio.h> #include <iostream> #include <fstream>  int main() {   std::ifstream a0;   a0.open("data/a0", std::ios::in | std::ios::binary);   double d;   a0 >> d;   printf("%e\n", d); } 

i compile with

g++ -s -wall -wextra -pedantic -std=c++0x -o program program.cpp 

but doesn't work - prints 0 (the actual first 8 bytes of file 3d 8f a0 bb e0 00 00 00). more interesting, when data/a0 file doesn't exist, garbage output, if file exist, output strictly 0.

what doing wrong?

if file binary, must use unformatted input functions it:

double d; if (!a0.read(reinterpret_cast<char*>(&d), sizeof(d))) {   // error occurred } std::cout << d << '\n'; 

operator >> formatted input, means expects text in file.

edit

sorry, used get() instead of read(), more useful reading text files in binary format.