Qt 5 Logging - definig category with QLoggingCategory -

i have problem qloggingcategory(const char * category).

when use like:

qstring rt = "3"; qstring sv = "p"; qloggingcategory dailylogger(qstring(rt+sv+"logger").tostdstring().c_str()); 

it doesn't work (my custom message handler doesn't recognize category).

but when use:

qloggingcategory dailylogger("3plogger"); 

message handler sees category.

here's handler function:

void mymessageoutput(qtmsgtype type, const qmessagelogcontext &context, const qstring &msg) {     if (qstring(context.category).contains("3"))     {         //some code     } } 

why computed category name not work?

qloggingcategory retains copy of char* pointer it's constructed. pointed-to characters must remain valid , constant life of qloggingcategory instance.

in failing example, c_str() returns temporary no longer valid after std::string goes out of scope. qloggingcategory pointing @ invalid memory (giving undefined behaviour).

in second example, pass string literal, valid lifetime of program, no lifetime issues arise.

you need copy string data char array lifetime outlives logging category.