boost scope exit

Boost.ScopeExit provides the macro BOOST_SCOPE_EXIT, which can be used to define something that looks like a local function but doesn't have a name. However, it does have a parameter list in parentheses and a block in braces.

#include <string>
#include <memory>
#include <cstdio>

struct CloseFile {
  void operator()(std::FILE* file) {
    std::fclose(file);
  }
};

void write_to_file(const std::string& s) {
  std::unique_ptr<std::FILE, CloseFile> file(std::fopen("hello-world.txt", "a"));
  std::fprintf(file.get(), s.c_str());
}

int main() {
  write_to_file("Hello, ");
  write_to_file("world!");
  return 0;
}

上述代码使用BOOST_SCOPE_EXIT，修改如下：

#include <string>
#include <memory>
#include <cstdio>
#include <boost/scope_exit.hpp>

void write_to_file(const std::string& s) {
  std::FILE* file = fopen("hello-world.txt", "a");
  BOOST_SCOPE_EXIT(&file)
  {
    std::fclose(file);
  }  BOOST_SCOPE_EXIT_END
  std::fprintf(file, s.c_str());
}

int main() {
  write_to_file("Hello, ");
  write_to_file("world!");
  return 0;
}