how measure complexity of program

Question

how does compiler determine there is run-time error ? Is it run the code and then decide whether code executable or not?

Another question: Are there any program which are capable to determine complexity of my executable code?

Are there any code which is for measuring the time when code start to execute up to finish?

Answer 1

Compilers don't determine if there is a run-time error, they handle syntax errors only. A run-time error is, by definition, something caught at the time of running the program.

The few tools I've used for measuring program complexity have been pretty useless. They tended to work on simple programs but most of the code we put through them either broke them or solicited inane suggestions (I'm pretty certain our code is as complex as it needs to be, and no more). But, for measuring run-time and resource usage of programs, you have a wide variety. Probably the most common is the time utility in UNIX and its brethren.

It actually runs the program inside a "wrapper" which measure elapsed and CPU times.

Alternatively, you can do on process accounting and collect all sorts of CPU, I/O and memory stats on all processes for later analysis.

Answer 2

Homework or not, you need to read up on the Halting problem if you think there are such algorithms that are guaranteed to work.

Hint: a program that could determine if another program will throw a runtime exception would solve the halting problem ...

Answer 3

The compiler doesn't determine run-time errors. The compiler is responsible for checking syntax errors, type-checking and other things. Run-time errors occur after the compiler has done it's job. An example would be checking an array with a subscript higher than the number of elements (segmentation fault). The operating system kills the program when it does this because the program could be trying to do something malicious (like over write other areas of memory that don't 'belong' to it) but in general its considered 'undefined behavior.'

I don't know of any programs that determine complexity but if there is it would probably be very specialized to specific cases.

and here's a code snippet of a simple timed program

#include <stdio.h>
#include <time.h>

int main() {

 clock_t before, after;

 before = clock();
 int i;
 for(i=0; i<1000; i++);
 after = clock();
 printf("%.2f seconds to run 1000 iterations of a blank for loop\n", (double)(after - before)/CLOCKS_PER_SEC);

 return 0;
}

Answer 4

If you are using a unix-like OS, you can use the time command to tell you just how much CPU time your program is taking.

Example:

The program:

#include <stdio.h>

int main(void)
{
   puts("Hello, world!");

   return 0;
}

The result:

tpost@tpost-desktop:~$ time ./hello
Hello, world!

real    0m0.001s
user    0m0.000s
sys     0m0.000s

Its handy to see of 'optimizations' are actually doing anything good.