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@samuelsmal
Created August 21, 2014 08:58
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c++ system call wrapper
#include <unistd.h>
#include <sys/socket.h>
// … and others for actual syscalls
#include <system_error>
#include <functional>
namespace sys
{
namespace
{
/// syscall actually has a return value
template<typename U, typename T, typename... Args>
struct syscall_wrapper
{
std::function<T (Args...)> _syscall;
syscall_wrapper (T syscall (Args...)) : _syscall (syscall) {}
U operator() (Args... args)
{
T const ret (_syscall (args...));
int const error_code (errno);
if (ret == T (-1))
{
throw std::system_error (error_code, std::system_category());
}
return U (ret);
}
};
/// syscall only has return value for error code
template<typename T, typename... Args>
struct syscall_wrapper<void, T, Args...>
{
std::function<T (Args...)> _syscall;
syscall_wrapper (T syscall (Args...)) : _syscall (syscall) {}
void operator() (Args... args)
{
T const ret (_syscall (args...));
int const error_code (errno);
if (ret == T (-1))
{
throw std::system_error (error_code, std::system_category());
}
}
};
/// helper to avoid having to list T and Args...
template<typename U, typename T, typename... Args>
syscall_wrapper<U, T, Args...> make_wrapper (T syscall (Args...))
{
return syscall_wrapper<U, T, Args...> (syscall);
}
}
/// return value has -1 but is of same type otherwise
int socket (int domain, int type, int protocol)
{
return make_wrapper<int> (&::socket) (domain, type, protocol);
}
/// return value is for error flagging only
void unlink (const char* pathname)
{
return make_wrapper<void> (&::unlink) (pathname);
}
/// return value would be of different type if not encoding errors in it
size_t read (int filedes, void* buf, size_t nbyte)
{
return make_wrapper<size_t> (&::read) (filedes, buf, nbyte);
}
}
/// usage example
// $ clang++ syscallwrap.cpp -o syscallwrap --std=c++11 && ./syscallwrap
// E: No such file or directory
#include <iostream>
int main (int, char**)
{
try
{
sys::unlink ("/hopefully_nonexisting_file");
}
catch (std::runtime_error const& ex)
{
std::cerr << "E: " << ex.what() << std::endl;
}
return 0;
}
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