在内部运行替换函数吗？

Question

if I am carrying out actions such as these on a classic ASP page:

if instr(tmp, "®") then tmp = replace(tmp, "®", "®")
if instr(tmp, "™") then tmp = replace(tmp, "™", "™")
if instr(tmp, "©") then tmp = replace(tmp, "©", "©")

is the replace function actually already doing an internal instr anyhow?? If so should the above code simply be changed to:

tmp = replace(tmp, "®", "®")
tmp = replace(tmp, "™", "™")
tmp = replace(tmp, "©", "©")

What is more resource efficient? They are being used in all sorts of scenarios such as being wrapped around user content in SQL statements etc...

Answer 1

With performance questions, the best answer is usually to benchmark. Fortunately, this situation is relatively easy to test:

Option Explicit

Const testString = "Some moderately long text string. Since I don't know long the actual input is, I'm just going to write some stuff. Oh, look, it's a special character! -> ®"

' Might want to start off with a lower number like 1000 and go up from there
Const numberOfIterations = 1000000

Dim replaceTime, inStrReplaceTime
Dim notReplaceTime, notInStrReplaceTime

' When search string is found in the target string
replaceTime = TestReplace("®")
inStrReplaceTime = TestInStrReplace("®")

' When search string is NOT found in the target string
notReplaceTime = TestReplace("©")
notInStrReplaceTime = TestInStrReplace("©")

WScript.Echo "Results (seconds, lower is better):" & vbNewline & _
    "  Replace: " & replaceTime & vbNewline & _
    "  InStr + Replace: " & inStrReplaceTime & vbNewline & _
    "  Replace (not in string): " & notReplaceTime & vbNewline & _
    "  InStr + Replace (not in string): " & notInStrReplaceTime & vbNewline

Function TestReplace(str)
    Dim startTime, i, outString

    startTime = Timer

    For i = 1 To numberOfIterations
        outString = Replace(testString, str, "something")
    Next

    TestReplace = Timer - startTime
End Function

Function TestInStrReplace(str)
    Dim startTime, i, outString

    startTime = Timer

    For i = 1 To numberOfIterations
        If InStr(testString, str) <> 0 Then outString = Replace(testString, str, "something")
    Next

    TestInStrReplace = Timer - startTime
End Function

On my machine, this script gave the output:

Results (seconds, lower is better):
  Replace: 0.8515625
  InStr + Replace: 1.234375
  Replace (not in string): 0.6796875
  InStr + Replace (not in string): 0.3046875

This may not be the most comprehensive test, but it does appear that the answer to which method is faster depends on whether or not you expect to see your search string in the string you are replacing.