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In C++11, this technique is known as generalized constant expressions (constexpr). [2] C++14 relaxes the constraints on constexpr – allowing local declarations and use of conditionals and loops (the general restriction that all data required for the execution be available at compile-time remains).
Its only purpose is to measure execution time (flat profiling), and to do this interactively from the debug console (i.e. on a single function). As it is said several times in this text; the timing is not accurate and it should only be used as a coarse measure of the approximate run time and load of a function.
In software engineering, profiling ("program profiling", "software profiling") is a form of dynamic program analysis that measures, for example, the space (memory) or time complexity of a program, the usage of particular instructions, or the frequency and duration of function calls.
64-bit and 32-bit applications, C, C++, .NET, and dlls generated by any language compiler. Performance and memory profiler that identifies time-intensive functions and detects memory leaks and errors. Proprietary gprof: Linux/Unix Any language supported by gcc: Several tools with combined sampling and call-graph profiling.
An experiment done in 1996 indicates that approximately 6–13% of execution time is spent simply dispatching to the correct function, though the overhead can be as high as 50%. [5] The cost of virtual functions may not be so high on modern CPU architectures due to much larger caches and better branch prediction.
Most compilers have at least the following compiler phases (which therefore occur at compile-time): syntax analysis, semantic analysis, and code generation.During optimization phases, constant expressions in the source code can also be evaluated at compile-time using compile-time execution, which reduces the constant expressions to a single value.
Function coverage will be satisfied if, during this execution, the function foo was called at least once. Statement coverage for this function will be satisfied if it was called for example as foo(1,1), because in this case, every line in the function would be executed—including z = x;.
When a program wants to time its own operation, it can use a function like the POSIX clock() function, which returns the CPU time used by the program. POSIX allows this clock to start at an arbitrary value, so to measure elapsed time, a program calls clock(), does some work, then calls clock() again. [1] The difference is the time needed to do ...