Understanding system_clock in C++ <chrono>: Differences Across Compilers
Understanding system_clock in C++ <chrono>: Differences Across Compilers
When dealing with time in modern C++ programming, the <chrono> library provides a set of high-precision time handling tools. A widely used clock type within this library is system_clock. However, developers may encounter subtle differences when compiling the same code with different compilers, particularly in terms of the default time unit for system_clock. This article explores this issue and offers solutions to handle it effectively.
Default Time Units in Different Compilers
GCC (g++-13)
In GCC, the default time unit for system_clock is nanoseconds (std::chrono::nanoseconds). This is defined as follows:
struct system_clock
{
typedef chrono::nanoseconds duration;
};Clang
In Clang, the default time unit for system_clock is microseconds (std::chrono::microseconds). It is defined as:
class _LIBCPP_TYPE_VIS system_clock
{
public:
typedef microseconds duration;
};This discrepancy means that when compiling the same code with different compilers, the precision and behavior of time calculations can vary.
But steady_clock is indeed consistent.
g++:
struct steady_clock
{
typedef chrono::nanoseconds duration;
}clang:
class _LIBCPP_TYPE_VIS steady_clock
{
public:
typedef nanoseconds duration;
}