Logger: A C++ repository from jokem59

Observations

Calling subsequent constructors on std::ofstream with the same file name result in any existing files with the same name being overwritten. This can be avoided by having timestamps associated with each log file.

ToDo

Add msbuild to system PATH
- C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\MSBuild\Current\Bin\amd64\msbuild.exe

CMake Learnings

Whichever directory 'cmake' is called from is where the build files will be generated.
- How do you specify where you want build files to go in CMakeLists.txt? You don't. CMake builds in whatever directory 'cmake' is called from
Top-level CMakeLists.txt can call sub-directory CMakeLists.txt by using add_subdirectory() command
- In this project, we call the add_subdirectory("./test") to build the unit test executable
Use target_include_directories command to specify where the compiler should look for header files to avoid doing things like: #include "../inc/Logger.h"
- The equivalent command for the linker to look for libraries is link_directories

C++ Learnings

Windows vs Linux

In Linux, the constructor:

Logger::Log::Log(std::string file) : filename{ file }
{
    auto now = Logger::GetTime();
    auto fullName =  now + "_" + filename;
    logFile = std::ofstream(fullName, std::ios::out); // Opens the file to write to

    inStr = std::stringstream("", std::ios_base::ate | std::ios_base::out | std::ios_base::in);
}

Successfully opens and writes to the specified log file name.

In Windows, this project builds and runs, but nothing is written to a file within the project's directories. When adding a test std::ofstream that is run as part of main() in LoggerUnitTest, a file is successfully written:

    std::ofstream ofs("test.txt", std::ios::out);
    ofs << "asd;lfkjalsdfj";
    ofs.close();

Files that are being created from the LogObject's constructor fail to create the file!

When hard coding a string in the Log constructor logFile.open("whatever"), the file opens successfully.

When using the class member variable filename, the file opens successfully as well. There's something about the temporary variable fullName that is causing issues.

SOLUTION: The date/time format was using illegal characters for Windows file names per Microsoft Docs. The colon : and forward slash / characters are reserved and attempting to open a file with those characters will fail.

Old date format: 2020/08/25_23:15:12.123
New date format: 2020.08.25-23.15.12.123

Using Copy Constructor that's Implicitly Delted

C:\Projects\Logger\src\Logger.cpp(34,1): error C2280: 'Logger::Log::Log(const Logger::Log &)': attempting to reference a deleted function [C:\Projects\Logger\build\Logger.vcxproj]

The copy constructor is used here.

// using implicitly created copy constructor which was deleted
Logger::Log foo = Logger::Log::Log("sample.log");

https://en.cppreference.com/w/cpp/language/copy_constructor

Copy constructor is deleted implicitly because:
- T has non-static data members that cannot be copied (have deleted, inaccessible, or ambiguous copy constructors)

http://www.cplusplus.com/reference/fstream/ofstream/ofstream/

std::ofstream deletes the copy constructor, therefore, my Log object implicitly deletes the copy constructor as well

Logger::Log foo = Logger::Log::Log("sample.log") semantically (before C++17) creates a temporary Logger::Log using the string, and then uses the copy constructor to initialise foo with that temporary - and even if the compiler elides the copy it is required to diagnose the semantic use of the copy constructor. From C++17, the temporary will be elided. Before C++17, the fix is to change the definition to Logger::Log foo ("sample.log")