Save errno before using sprintf, ifstream.

std::ifstream in libstdc++ contains a bug, where it sets errno to zero.
To work around it, we manually save the errno before using std::ifstream
in debugger check, and reset it after we are done.

We also preventively save errno before using sprintf.

Fixes #835

CMakeLists.txt

@@ -135,6 +135,7 @@ set(INTERNAL_HEADERS
         ${HEADER_DIR}/internal/catch_debugger.h
         ${HEADER_DIR}/internal/catch_debugger.hpp
         ${HEADER_DIR}/internal/catch_default_main.hpp
+        ${HEADER_DIR}/internal/catch_errno_guard.hpp
         ${HEADER_DIR}/internal/catch_evaluate.hpp
         ${HEADER_DIR}/internal/catch_exception_translator_registry.hpp
         ${HEADER_DIR}/internal/catch_expression_lhs.hpp

include/internal/catch_debugger.hpp

@@ -10,6 +10,7 @@
 #define TWOBLUECUBES_CATCH_DEBUGGER_HPP_INCLUDED
 
 #include "catch_debugger.h"
+#include "catch_errno_guard.hpp"
 
 #ifdef CATCH_PLATFORM_MAC
 
@@ -72,6 +73,9 @@
         // be strace, for example) in /proc/$PID/status, so just get it from
         // there instead.
         bool isDebuggerActive(){
+            // Libstdc++ has a bug, where std::ifstream sets errno to 0
+            // This way our users can properly assert over errno values
+            ErrnoGuard guard;
             std::ifstream in("/proc/self/status");
             for( std::string line; std::getline(in, line); ) {
                 static const int PREFIX_LEN = 11;

include/internal/catch_errno_guard.hpp

@@ -0,0 +1,25 @@
+/*
+ *  Created by Martin on 06/03/2017.
+ *
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+#ifndef TWOBLUECUBES_CATCH_ERRNO_GUARD_HPP_INCLUDED
+#define TWOBLUECUBES_CATCH_ERRNO_GUARD_HPP_INCLUDED
+
+#include <cerrno>
+
+
+namespace Catch {
+
+    class ErrnoGuard {
+    public:
+        ErrnoGuard():m_oldErrno(errno){}
+        ~ErrnoGuard() { errno = m_oldErrno; }
+    private:
+        int m_oldErrno;
+    };
+
+}
+
+#endif // TWOBLUECUBES_CATCH_ERRNO_GUARD_HPP_INCLUDED

include/reporters/catch_reporter_bases.hpp

@@ -9,6 +9,7 @@
 #define TWOBLUECUBES_CATCH_REPORTER_BASES_HPP_INCLUDED
 
 #include "../internal/catch_interfaces_reporter.h"
+#include "../internal/catch_errno_guard.hpp"
 
 #include <cstring>
 #include <cfloat>
@@ -27,6 +28,9 @@ namespace Catch {
             // + 1 for null terminator
             const size_t maxDoubleSize = DBL_MAX_10_EXP + 1 + 1 + 3 + 1;
             char buffer[maxDoubleSize];
+            
+            // Save previous errno, to prevent sprintf from overwriting it
+            ErrnoGuard guard;
 #ifdef _MSC_VER
             sprintf_s(buffer, "%.3f", duration);
 #else