Suppose that there exists a big-sized string, and I would pass this string variable into a specific function. What will be the best way for speed?

[Test]

1. Make 10,000,000 byte length string variable.

#define STRING_SIZE 10000000

string s;

for (int i = 0; i < STRING_SIZE; i++)

  s += rand() % 256;

2. Pass this s string parameter into the following functions. Of course, s variable value does not change in each function.

#define SUB_STR     "ABCDE"

size_t find_string                (const string s)  { return s.find(SUB_STR);  }

size_t find_const_string          (const string s)  { return s.find(SUB_STR);  }

size_t find_pointer_string        (string* s)       { return s->find(SUB_STR); }

size_t find_const_pointer_string  (const string* s) { return s->find(SUB_STR); }

size_t find_reference_string      (string& s)       { return s.find(SUB_STR);  }

size_t find_const_reference_string(const string& s) { return s.find(SUB_STR);  }

3. Measure the elapsed time to complete the loop.

#define COUNT       100

begTick = timeGetTime();

for(i = 0; i < COUNT; i++)

  find_string(s);

endTick = timeGetTime();

printf("find_string                 elapsed %u msec\n", endTick - begTick);

[Result]

Microsoft Visual Studio 2005 Relase mode. Optimization - Maximize Speed (/O2)

find_string                 elapsed 2257 msec

find_const_string           elapsed 2244 msec

find_pointer_string         elapsed 733 msec

find_const_pointer_string   elapsed 733 msec

find_reference_string       elapsed 732 msec

find_const_reference_string elapsed 733 msec

[Conslusion]

Keyword  "const" does not result in an optimization code for a big-sized string parameter.

If a big-sized string variable should be passed into a function, pointer or reference type is desirable.

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