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Estimation of a condition in a cycle?

string strLine;//not constant
int index = 0;
while(index < strLine.length()){//strLine is not modified};

how many times is estimated strLine.length()

whether to use nLengthwith nLengthassigned strLine.length()just before the loop

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9 answers

lengthwill be evaluated every time you go through the loop, however, since it lengthis a constant time ( O(1)), it does not matter much, and adding a variable to store this value is likely to have little effect with a small hit on reading the code (as well as breaking the code if the string is ever changed).

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string strLine;
int stringLength = strLine.length();
int index = 0;
while(index < stringLength);
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strLine.length() (i < strLine.length())

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string strLine;//not constant
int index = 0;
const int strLenght = strLine.Length();
while(index < strLine.length()){//strLine is not modified};

, Length().

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int main()
{
    std::string strLine="hello world";

    for (int i=0; i < strLine.length(); ++i)
    {
        std::cout << strLine[i] <<std::endl;
    }
}

:

    for (int i=0; i < strLine.length(); ++i)
0040104A  cmp         dword ptr [esp+20h],esi 
0040104E  jbe         main+86h (401086h)


 std::string strLine="hello world";
 const int strLength = strLine.length();
 for (int i=0; i < strLength ; ++i)
 {
    std::cout << strLine[i] <<std::endl;
 }

:

   for (int i=0; i < strLength ; ++i)
0040104F  cmp         edi,esi 
00401051  jle         main+87h (401087h)

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Since you are not changing the line, should you not use

const string strLine;

Simple, because then the compiler gets some additional information about what can and cannot change, but I'm not sure how smart the C ++ compiler can get.

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strLine.length() will be evaluated every time you go around the loop.

You are right that it would be more efficient to use nLength, especially if it is strLinelong.

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