CODEWITHSUNDEEP
multithreadingc++11
Swiss Frank
Swiss Frank

Reputation: 2422

how to printf() std::this_thread::get_id() in C++?

I've tried to cast to void* and use %p. I've also tried intptr_t with a format of %lx. Both times I get the "Invalid Cast" error.

I'm using -Wall -Werror which checks that the arguments of the printf() match the function's format string. So I can't merely count on get_id() leaving a 4- or 8-byte value on the stack and simply printing that value as hex.

I'm using gcc version 9.2.1 20190827 (Red Hat 9.2.1-1) (GCC)

The OS is Fedora release 31 (Thirty One) . The CPU is 64-bit Intel x86.

Upvotes: 5

Views: 11192

Answers (2)

tim.n.braun
tim.n.braun

Reputation: 11

I was able to use this work-around in a logging function that had similar requirments:

static std::ostringstream id;
static std::string sid = id.str();

if (sid.empty())
{
    id << std::this_thread::get_id();
    sid = id.str();
}

// our code actually has a vsnprintf() 
printf("[%u:%s] %s", getpid(),  
        sid.c_str(), another_string );

Same mechanism as answer 1. The thread id type is quite opaque.

Upvotes: 1

rafix07
rafix07

Reputation: 20938

Use streams:

std::ostringstream oss;
oss << std::this_thread::get_id() << std::endl;
printf("%s\n", oss.str().c_str());

Upvotes: 9

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