I am having some trouble writing the constructor for my UniquePtr class.
Here is the UniquePtr constructor
UniquePtr::UniquePtr(Foo *ptr) {
_ptr = ptr;
Foo(myStr);
}
Here is the Foo constructor
Foo::Foo( const string& tag ) : _serial{++_count}, _tag{tag} {
// If tag is empty, set it to the serial number
cout << "* c-tor - Foo S#: " << _serial
<< ( _tag.length( ) > 0 ? " Tag: " : "" ) << _tag << "\n";
}
And this is the instruction for what I need to do: "Modify your constructor so that it will actually perform the memory allocation step during construction. Since the Foo class’s constructor takes an optional std::string argument, your new UniquePtr constructor should do the same. This parameter should default to the empty string. Pass the value from the UniquePtr constructor directly into the Foo constructor when you allocate the new object."
What I should do with my constructor right now?
Related
In C++ I can do the following:
class foo {
private:
int N;
public:
foo(const int pN) {
N = pN;
std::cout << N << std::endl;
}
};
or, with the concept of outer constructors in Julia in mind,
class foo {
private:
int N;
};
foo::foo(const int pN) {
N = pN;
std::cout << N << std::endl;
}
Can you do the same in Julia, i.e., set some member variables and then do something with them? Consider the MWE below:
struct foo
N::Int
function foo(pN::Int)
new(pN)
println("Hello World") # Gets printed
println(N) # ERROR: LoadError: UndefVarError: N not defined
end
end
Why is that and how do I deal with this?
Even more strange is the behaviour for outer constructors:
struct foo
N::Int
end
function foo(pN::Int)
println("Hello World") # Not shown
foo(pN)
println("Hello World") # Not shown
println(N) # No error
end
although I get the warning that the outer constructor overwrites the "default" one - so I suspected that I would at least see something, either print message or Error.
There is no scope. Julia does not have object oriented programming facilities. Store the result of new as self and access the value of N as a field of self.
julia> struct foo
N::Int
function foo(pN::Int)
self = new(pN)
println("Hello World")
println(self.N)
self
end
end
julia> foo(5)
Hello World
foo(5)
Your second example results in a stack overflow.
I am learning from http://www.cochoy.fr/boost-property-tree/.
Instead of write_json to stdout, I tried to save it in a string.
std::stringstream ss;
boost::property_tree::json_parser::write_json(ss, oroot, false);
std::cout <<" begin json string" << std::endl;
std::cout << ss.str() << std::endl;
std::cout << "after json string" << std::endl;
output:
begin json string
{"height":"320","some":{"complex":{"path":"bonjour"}},"animals":{"rabbit":"white","dog":"brown","cat":"grey"},"fish":"blue","fish":"yellow","fruits":["apple","raspberry","orange"],"matrix":[["1","2","3"],["4","5","6"],["7","8","9"]]}
after json string
According to the output above, there is a new empty line at the end. How to get rid of the new line? Because with the new line it is not a valid JSON string.
The newline is not explicitly mentioned in the JSON RFC-7159 but it is defined as part of the POSIX standard for a line.
Incase you're interested in where the newline comes from you can take a look at the write_json_internal source code, we can see that there is an stream << std::endl; near the end of the method. Note that ...::write_json references write_json_internal.
// Write ptree to json stream
template<class Ptree>
void write_json_internal(std::basic_ostream<typename Ptree::key_type::value_type> &stream,
const Ptree &pt,
const std::string &filename,
bool pretty)
{
if (!verify_json(pt, 0))
BOOST_PROPERTY_TREE_THROW(json_parser_error("ptree contains data that cannot be represented in JSON format", filename, 0));
write_json_helper(stream, pt, 0, pretty);
stream << std::endl;
if (!stream.good())
BOOST_PROPERTY_TREE_THROW(json_parser_error("write error", filename, 0));
}
I have a simple c++ program
main.cpp
#include <iostream>
using namespace std;
int addition (int a, int b)
{
int r;
r=a+b;
return r;
}
int main ()
{
int z;
z = addition (5,3);
cout << "The result is " << z;
}
I want to generate the function tracing for this
- print function names and its input output and return types
My systemtap script : para-callgraph.stp
#! /usr/bin/env stap
function trace(entry_p, extra) {
%( $# > 1 %? if (tid() in trace) %)
printf("%s%s%s %s\n",
thread_indent (entry_p),
(entry_p>0?"->":"<-"),
probefunc (),
extra)
}
probe $1.call { trace(1, $$parms) }
probe $1.return { trace(-1, $$return) }
My C++ Exec is called : a ( compiled as g++ -g main.cpp)
Command I run
stap para-callgraph.stp 'process("a").function("*")' -c "./a > /dev/null"
0 a(15119):->_GLOBAL__I__Z8additionii
27 a(15119): ->__static_initialization_and_destruction_0 __initialize_p=0x0 __priority=0x0
168 a(15119): <-__static_initialization_and_destruction_0
174 a(15119):<-_GLOBAL__I__Z8additionii
0 a(15119):->main
18 a(15119): ->addition a=0x0 b=0x400895
30 a(15119): <-addition return=0x8
106 a(15119):<-main return=0x0
Here ->addition a=0x0 b=0x400895 : its address and not actual values ie 5, 3 which I want.
How to modify my stap script?
This appears to be a systemtap bug. It should print the value of b, not its address. Please report it to the systemtap#sourceware.org mailing list (with compiler/etc. versions and other info, as outlined in man error::reporting.
As to changing the script, the $$parms part is where the local variables are being transformed into a pretty-printed string. It could be changed to something like...
trace(1, $$parms . (#defined($foobar) ? (" foobar=".$foobar$) : ""))
to append foobar=XYZ to the trace record, whereever a parameter foobar is available. To work around the systemtap bug in question, you could try
trace(1, $$parms . (#defined($b) ? (" *b=".user_int($b)) : ""))
to dereference the b variable as if it were an int *.
Can I use LineID attribute for this?
I hope I could use sink::set_formatter to do this instead of using
__LINE__
and
__FILE__
in each log statement.
I struggled with this, until I found this snippet
#define LFC1_LOG_TRACE(logger) \
BOOST_LOG_SEV(logger, trivial::trace) << "(" << __FILE__ << ", " << __LINE__ << ") "
Works like a charm
The LineID attribute is a sequential number that is incremented for each logging message. So you can't use that.
You can use attributes to log the line numbers etc. This allows you flexible formatting using the format string, whereas using Chris' answer your format is fixed.
Register global attributes in your logging initialization function:
using namespace boost::log;
core::get()->add_global_attribute("Line", attributes::mutable_constant<int>(5));
core::get()->add_global_attribute("File", attributes::mutable_constant<std::string>(""));
core::get()->add_global_attribute("Function", attributes::mutable_constant<std::string>(""));
Setting these attributes in your logging macro:
#define logInfo(methodname, message) do { \
LOG_LOCATION; \
BOOST_LOG_SEV(_log, boost::log::trivial::severity_level::info) << message; \
} while (false)
#define LOG_LOCATION \
boost::log::attribute_cast<boost::log::attributes::mutable_constant<int>>(boost::log::core::get()->get_global_attributes()["Line"]).set(__LINE__); \
boost::log::attribute_cast<boost::log::attributes::mutable_constant<std::string>>(boost::log::core::get()->get_global_attributes()["File"]).set(__FILE__); \
boost::log::attribute_cast<boost::log::attributes::mutable_constant<std::string>>(boost::log::core::get()->get_global_attributes()["Function"]).set(__func__);
Not exactly beautiful, but it works and it was a long way for me. It's a pity boost doesn't offer this feature out of the box.
The do {... } while(false) is to make the macro semantically neutral.
The solution shown by Chris works, but if you want to customize the format or choose which information appears in each sink, you need to use mutable constant attributes:
logging::core::get()->add_global_attribute("File", attrs::mutable_constant<std::string>(""));
logging::core::get()->add_global_attribute("Line", attrs::mutable_constant<int>(0));
Then, you make a custom macro that includes these new attributes:
// New macro that includes severity, filename and line number
#define CUSTOM_LOG(logger, sev) \
BOOST_LOG_STREAM_WITH_PARAMS( \
(logger), \
(set_get_attrib("File", path_to_filename(__FILE__))) \
(set_get_attrib("Line", __LINE__)) \
(::boost::log::keywords::severity = (boost::log::trivial::sev)) \
)
// Set attribute and return the new value
template<typename ValueType>
ValueType set_get_attrib(const char* name, ValueType value) {
auto attr = logging::attribute_cast<attrs::mutable_constant<ValueType>>(logging::core::get()->get_global_attributes()[name]);
attr.set(value);
return attr.get();
}
// Convert file path to only the filename
std::string path_to_filename(std::string path) {
return path.substr(path.find_last_of("/\\")+1);
}
The next complete source code create two sinks. The first uses File and Line attributes, the second not.
#include <boost/log/trivial.hpp>
#include <boost/log/sources/severity_logger.hpp>
#include <boost/log/utility/setup/file.hpp>
#include <boost/log/utility/setup/console.hpp>
#include <boost/log/expressions.hpp>
#include <boost/log/utility/setup/common_attributes.hpp>
#include <boost/log/attributes/mutable_constant.hpp>
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <boost/log/support/date_time.hpp>
#include <boost/log/attributes/mutable_constant.hpp>
namespace logging = boost::log;
namespace attrs = boost::log::attributes;
namespace expr = boost::log::expressions;
namespace src = boost::log::sources;
namespace keywords = boost::log::keywords;
// New macro that includes severity, filename and line number
#define CUSTOM_LOG(logger, sev) \
BOOST_LOG_STREAM_WITH_PARAMS( \
(logger), \
(set_get_attrib("File", path_to_filename(__FILE__))) \
(set_get_attrib("Line", __LINE__)) \
(::boost::log::keywords::severity = (boost::log::trivial::sev)) \
)
// Set attribute and return the new value
template<typename ValueType>
ValueType set_get_attrib(const char* name, ValueType value) {
auto attr = logging::attribute_cast<attrs::mutable_constant<ValueType>>(logging::core::get()->get_global_attributes()[name]);
attr.set(value);
return attr.get();
}
// Convert file path to only the filename
std::string path_to_filename(std::string path) {
return path.substr(path.find_last_of("/\\")+1);
}
void init() {
// New attributes that hold filename and line number
logging::core::get()->add_global_attribute("File", attrs::mutable_constant<std::string>(""));
logging::core::get()->add_global_attribute("Line", attrs::mutable_constant<int>(0));
// A file log with time, severity, filename, line and message
logging::add_file_log (
keywords::file_name = "sample.log",
keywords::format = (
expr::stream
<< expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y-%m-%d_%H:%M:%S.%f")
<< ": <" << boost::log::trivial::severity << "> "
<< '[' << expr::attr<std::string>("File")
<< ':' << expr::attr<int>("Line") << "] "
<< expr::smessage
)
);
// A console log with only time and message
logging::add_console_log (
std::clog,
keywords::format = (
expr::stream
<< expr::format_date_time< boost::posix_time::ptime >("TimeStamp", "%Y-%m-%d %H:%M:%S")
<< " | " << expr::smessage
)
);
logging::add_common_attributes();
}
int main(int argc, char* argv[]) {
init();
src::severity_logger<logging::trivial::severity_level> lg;
CUSTOM_LOG(lg, debug) << "A regular message";
return 0;
}
The statement CUSTOM_LOG(lg, debug) << "A regular message"; generates two outputs, writing a log file with this format...
2015-10-15_15:25:12.743153: <debug> [main.cpp:61] A regular message
...and outputs to the console this:
2015-10-15 16:58:35 | A regular message
Another possibility is to add line and file attributes to each log record after they are created. This is possible since in newer releases. Attributes added later do not participate in filtering.
Assuming severity_logger identified with variable logger:
boost::log::record rec = logger.open_record(boost::log::keywords::severity = <some severity value>);
if (rec)
{
rec.attribute_values().insert(boost::log::attribute_name("Line"),
boost::log::attributes::constant<unsigned int>(__LINE__).get_value());
... other stuff appended to record ...
}
The above would, of course, get wrapped into convenient macro.
Later you can show this attribute using custom formatter for the sink:
sink->set_formatter( ...other stuff... << expr::attr<unsigned int>("Line") << ...other stuff... );
Unlike previous answer, this approach requires more custom code and can't use off-the-shelf boost logging macros.
For posterity's sake - I made this set of macros for very simple logging needs, which has served me well - for simple logging needs. But they illustrate how to do this in general, and the concept easily works with Boost. They are meant to be local to one file (which is running in multiple processes, sometimes in multiple threads in multiple processes). They are made for relative simplicity, not speed. They are safe to put in if statements etc. to not steal the else. At the beginning of a function in which one wants to log, one calls
GLogFunc("function name");
Then one can do this to log a complete line:
GLogL("this is a log entry with a string: " << some_string);
They are as so -
#define GLogFunc(x) std::stringstream logstr; \
std::string logfunc; \
logfunc = x
#define GLog(x) do { logstr << x; } while(0)
#define GLogComplete do { \
_log << "[PID:" << _my_process << " L:" << __LINE__ << "] ((" << logfunc << ")) " << logstr.str() << endl; \
logstr.str(""); \
_log.flush(); \
} while(0)
#define GLogLine(x) do { GLog(x); GLogComplete; } while(0)
#define GLogL(x) GLogLine(x)
#define GLC GLogComplete
One can also build up a log over a few lines...
GLog("I did this.");
// later
GLog("One result was " << some_number << " and then " << something_else);
// finally
GLog("And now I'm done!");
GLogComplete;
Whatever stream _log is (I open it as a file in the class constructor, which is guaranteed to be safe in this instance) gets ouput like this:
[PID:4848 L:348] ((SetTextBC)) ERROR: bad argument row:0 col:-64
And they can be conditionally turned off and all performance penalty negated by a symbol at compilation time like so:
#ifdef LOGGING_ENABLED
... do the stuff above ...
#else
#define GLogFunc(x)
#define GLog(x)
#define GLogComplete
#define GLogLine(x)
#define GLogL(x)
#endif
Here is my solution.
Setup code
auto formatter =
expr::format("[ %3% %1%:%2% :: %4%]")
% expr::attr< std::string >("File")
% expr::attr< uint32_t >("Line")
% expr::attr< boost::posix_time::ptime >("TimeStamp")
% expr::smessage
;
/* stdout sink*/
boost::shared_ptr< sinks::text_ostream_backend > backend =
boost::make_shared< sinks::text_ostream_backend >();
backend->add_stream(
boost::shared_ptr< std::ostream >(&std::clog, NullDeleter()));
// Enable auto-flushing after each log record written
backend->auto_flush(true);
// Wrap it into the frontend and register in the core.
// The backend requires synchronization in the frontend.
typedef sinks::synchronous_sink< sinks::text_ostream_backend > sink2_t;
boost::shared_ptr< sink2_t > sink_text(new sink2_t(backend));
logging::add_common_attributes();
sink_text->set_formatter(formatter);
The log usage code (short version):
rec.attribute_values().insert("File", attrs::make_attribute_value(std::string(__FILE__))); \
full version :
#define LOG(s, message) { \
src::severity_logger< severity_level > slg; \
logging::record rec = slg.open_record(keywords::severity = s); \
if (rec) \
{ \
rec.attribute_values().insert("File", attrs::make_attribute_value(boost::filesystem::path(__FILE__).filename().string())); \
rec.attribute_values().insert("Line", attrs::make_attribute_value(uint32_t(__LINE__))); \
logging::record_ostream strm(rec); \
strm << message; \
strm.flush(); \
slg.push_record(boost::move(rec)); \
} \
}\
If I define global attribute (like people adviced before), i.e.
logging::core::get()->add_global_attribute("File", attrs::mutable_constant<std::string>(""));
then I get empty files/stiring.
I prefer to work with std::string but I like to figure out what is going wrong here.
I am unable to understand out why std::find isn't working properly for type T** even though pointer arithmetic works on them correctly. Like -
std::cout << *(argv+1) << "\t" <<*(argv+2) << std::endl;
But it works fine, for the types T*[N].
#include <iostream>
#include <algorithm>
int main( int argc, const char ** argv )
{
std::cout << *(argv+1) << "\t" <<*(argv+2) << std::endl;
const char ** cmdPtr = std::find(argv+1, argv+argc, "Hello") ;
const char * testAr[] = { "Hello", "World" };
const char ** testPtr = std::find(testAr, testAr+2, "Hello");
if( cmdPtr == argv+argc )
std::cout << "String not found" << std::endl;
if( testPtr != testAr+2 )
std::cout << "String found: " << *testPtr << std::endl;
return 0;
}
Arguments passed: Hello World
Output:
Hello World
String not found
String found: Hello
Thanks.
Comparing types of char const* amounts to pointing to the addresses. The address of "Hello" is guaranteed to be different unless you compare it to another address of the string literal "Hello" (in which case the pointers may compare equal). Your compare() function compares the characters being pointed to.
In the first case, you're comparing the pointer values themselves and not what they're pointing to. And the constant "Hello" doesn't have the same address as the first element of argv.
Try using:
const char ** cmdPtr = std::find(argv+1, argv+argc, std::string("Hello")) ;
std::string knows to compare contents and not addresses.
For the array version, the compiler can fold all literals into a single one, so every time "Hello" is seen throughout the code it's really the same pointer. Thus, comparing for equality in
const char * testAr[] = { "Hello", "World" };
const char ** testPtr = std::find(testAr, testAr+2, "Hello");
yields the correct result