I need a class to wrap calls to std::clog so that:
std::clog << "..." for all its features (i.e. the ability to have implicit basic type-to-string conversions, stream manipulators, flushing, etc.) My attempt has been based on many examples found in this forum (*), but I guess in a kind of a wrong way, because my class is a bit faulty.
Essentially what I tried is to extend std::streambuf by overriding the overflow and xputn methods in a way that they end up calling clog's operator<<.
NB: I found it difficult to keep my question complete(**), minimal and verifiable all at the same time, so any suggestions/comments on that will be much appreciated. What matters most to me, though, is the approach I have taken rather than the specific bugs or implementation flaws.
class LogStream : public std::streambuf
{
public:
enum class Color { RED_BRIGHT, RED_DARK, /* ...others */ NO_COLOR };
LogStream(void);
LogStream(std::basic_ostream<char>& out, std::string cname, char c, Color icon_color, Color text_color = Color::NO_COLOR);
/* Non-copiable. */
LogStream(const LogStream&) = delete;
LogStream& operator=(const LogStream&) = delete;
static void setNameLength(int l);
protected:
int_type overflow(int_type c = traits_type::eof());
std::streamsize xsputn(const char* s, std::streamsize n);
private:
/* Important stuff: */
std::basic_ostream<char>& m_out;
bool m_new_line;
void conditionalPrintHeader(void);
void endLine(void);
/* For message decoration purposes: */
Color m_color_icon;
Color m_color_text;
char m_icon;
std::string m_cname;
static std::map<Color, const std::string> m_color_lut;
};
/* A macro to create static instances of a logger later in each CPP file. */
#define CREATE_LOGGER(klass) \
namespace Log { \
static std::ostream dbg(new LogStream( \
std::clog, \
#klass, \
'>', \
LogStream::Color::RED_BRIGHT, \
LogStream::Color::NO_COLOR)); \
static std::ostream err(new LogStream( \
std::clog, \
#klass, \
'e', \
LogStream::Color::RED_BRIGHT, \
LogStream::Color::RED_DARK)); \
}
My overridden functions are implemented like so:
std::streamsize LogStream::xsputn(const char* s, std::streamsize n)
{
conditionalPrintHeader();
if(s[n - 1] == '\n') {
m_new_line = true;
endLine();
}
m_out << s;
return n;
}
LogStream::int_type LogStream::overflow(int_type c)
{
if(c == traits_type::eof()) {
return traits_type::eof();
} else {
char_type ch = traits_type::to_char_type(c);
return xsputn(&ch, 1) == 1 ? c : traits_type::eof();
}
}
void LogStream::conditionalPrintHeader(void)
{
if(m_new_line) {
m_out << "... header and color escape codes ...";
m_new_line = false;
}
}
void LogStream::endLine(void)
{
m_out << "color escape code for no color.";
}
The functions conditionalPrintHeader and endLine essentially try to implement this basic structure:
[header string] [ANSI color code] [<the log message>] [end color code]
So that when I do:
Log::warn << "Integer: " << 123 << ", Bool: " << std::boolalpha << true << ", Float: " << 3.1415f << "\n";
The terminal outputs:
HEADER + [START COLOR] Integer: 123, Bool: true, Float: 3.1415 [END COLOR]
Most of the time everything works great except when I need to print integer values. Instead of the number, I get additional garbage, like so:
[ ... ] Integer: 123�~c, Bool: true, Float: 3.1415
Notes:
(*) Similar questions that inspired or directly contributed to my solution:
(**) I pasted the whole header and source files in order to be as complete as possible and in case I'm missing the error somewhere else: Log.hpp, Log.cpp.
For now I considered that the problem laid in the character string argument of xsputn (which I assumed is not null-terminated). I solved my issue with integers like as follows, but I'm still unclear whether the approach is good or not.
std::streamsize LogStream::xsputn(const char* s, std::streamsize n)
{
conditionalPrintHeader();
if(s[n - 1] == '\n') {
m_new_line = true;
endLine();
}
std::string str;
for(int c = 0; c < n; c++) {
str += s[c];
}
m_out << str;
return n;
}