log.cpp

#include <cstdint>
#include <cinttypes>
#include <cstdio>
#include <cstdarg>
#include <iostream>

void log(const char * file_name, uint64_t line_number, const char * function_name, const char * format, ...)
{
	char buffer[21];
	int written = snprintf(buffer, sizeof(buffer), "[%s(%" PRIu64 ")]@%s:", file_name, line_number, function_name);
	if(written < 0 || written >= sizeof(buffer))
	{
		fprintf(stderr, "header over %d\n", written);
		return ;
	}

	va_list args;
	va_start(args, format);
	int result = vsnprintf(buffer + written, sizeof(buffer) - written, format, args);
	va_end(args);

	if(result < 0 || (written + result) >= sizeof(buffer))
	{
		fprintf(stderr, "contents over (%d, %d)\n", written, result);
		return ;
	}

	printf("%s", buffer);
}

namespace A
{
	void B()
	{
		log(__FILE__, __LINE__, __func__, "Hello, A::B()\n");
	}
}

int main(int argc, char * argv[])
{
	log(__FILE__, __LINE__, __func__, "Hello, Log\n");

	A::B();

	return 0;
}