C++:Tip

lastmod 2019-01-07created 2015-03-056 edits

Which loop has better performance

• Stackoverflow: Which loop has better performance? Increment or decrement?

for (int i=0;i<=10;i++) {
    /* This is better? */
}
for (int i=10;i>=0;i--) {
    /* This is better? */
}

Incrementing and decrementing (INC and DEC, when translated into assembler commands) have the same speed of 1 CPU cycle.

However, the second can be theoretically faster on some (e.g. SPARC) architectures because no 10 has to be fetched from memory (or cache): most architectures have instructions that deal in an optimized fashion when compating with the special value 0 (usually having a special hardwired 0-register to use as operand, so no register has to be "wasted" to store the 10 for each iteration's comparison).

A smart compiler (especially if target instruction set is RISC) will itself detect this and (if your counter variable is not used in the loop) apply the second "decrement downto 0" form.

Please see answers https://stackoverflow.com/a/2823164/1018783 and https://stackoverflow.com/a/2823095/1018783 for further details.

Debugging Interrupt

Raising an interrupt with inline assembly code like the following lets you start debugging right away.

__asm { int 3 };

Execute file path

• Stackoverflow: Finding current executable's path

Ways to find the path of the running EXE file, by OS:

• Mac OS X: _NSGetExecutablePath() (man 3 dyld)
• Linux: readlink /proc/self/exe
• Solaris: getexecname()
• FreeBSD: sysctl CTL_KERN KERN_PROC KERN_PROC_PATHNAME -1
• FreeBSD if it has procfs: readlink /proc/curproc/file (FreeBSD doesn't have procfs by default)
• NetBSD: readlink /proc/curproc/exe
• DragonFly BSD: readlink /proc/curproc/file
• Windows: GetModuleFileName() with hModule = NULL

See also

• C++
• Program optimization

Favorite site

• [https://docs.microsoft.com/en-us/previous-versions/ms364057(v=vs.80 MSDN - Named Return Value Optimization in Visual C++ 2005]