common: Move error handling to error.cpp/h

This allows us to avoid implicitly including <string> every time common_funcs.h is included.

src/common/error.cpp

@@ -0,0 +1,56 @@
+// Copyright 2013 Dolphin Emulator Project / 2014 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <cstddef>
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <cerrno>
+#include <cstring>
+#endif
+
+#include "common/error.h"
+
+namespace Common {
+
+std::string NativeErrorToString(int e) {
+#ifdef _WIN32
+    LPSTR err_str;
+
+    DWORD res = FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER |
+                                   FORMAT_MESSAGE_IGNORE_INSERTS,
+                               nullptr, e, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                               reinterpret_cast<LPSTR>(&err_str), 1, nullptr);
+    if (!res) {
+        return "(FormatMessageA failed to format error)";
+    }
+    std::string ret(err_str);
+    LocalFree(err_str);
+    return ret;
+#else
+    char err_str[255];
+#if defined(__GLIBC__) && (_GNU_SOURCE || (_POSIX_C_SOURCE < 200112L && _XOPEN_SOURCE < 600))
+    // Thread safe (GNU-specific)
+    const char* str = strerror_r(e, err_str, sizeof(err_str));
+    return std::string(str);
+#else
+    // Thread safe (XSI-compliant)
+    int second_err = strerror_r(e, err_str, sizeof(err_str));
+    if (second_err != 0) {
+        return "(strerror_r failed to format error)";
+    }
+    return std::string(err_str);
+#endif // GLIBC etc.
+#endif // _WIN32
+}
+
+std::string GetLastErrorMsg() {
+#ifdef _WIN32
+    return NativeErrorToString(GetLastError());
+#else
+    return NativeErrorToString(errno);
+#endif
+}
+
+} // namespace Common