Print more information when a system_error is caught

Author: WardBrian

src/cmdstan/file.hpp

@@ -272,7 +272,7 @@ std::ifstream safe_open(const std::string &fname) {
 std::unique_ptr<std::ofstream> safe_create(const std::string &fname,
                                            int sig_figs) {
   auto ofs = std::make_unique<std::ofstream>(fname.c_str());
-  ofs->exceptions(std::ofstream::badbit);
+  ofs->exceptions(std::ofstream::badbit | std::ofstream::failbit);
   if (sig_figs > -1) {
     ofs->precision(sig_figs);
   }

src/cmdstan/main.cpp

@@ -1,3 +1,7 @@
+#include <stdexcept>
+#include <iostream>
+#include <cerrno>
+
 #include <cmdstan/command.hpp>
 #include <stan/services/error_codes.hpp>
 
@@ -8,6 +12,11 @@ int main(int argc, const char *argv[]) {
       return cmdstan::return_codes::OK;
     else
       return cmdstan::return_codes::NOT_OK;
+  } catch (std::system_error &e) {
+    // system_error is thrown by std::ofstream but the
+    // message is not always helpful, so we also print errno
+    std::cerr << e.what() << ": " << std::strerror(errno) << std::endl;
+    return cmdstan::return_codes::NOT_OK;
   } catch (const std::exception &e) {
     std::cerr << e.what() << std::endl;
     return cmdstan::return_codes::NOT_OK;