A sub for trimming alphabet in a string

[Takase]

I found a topic about trimming characters in a string in the forum before. But I've lost the link to the topic and I'm lazy to find it again. So, I wrote myself a little piece of code to trim a specified alphabet from a string.
It is basically "trim()" but it runs through the string to trim all the matching alphabet in the string instead of only trimming the matching alphabet at the leftmost side and the rightmost side of the string. I hope this will help somebody.

Note: Edited a little bit. Instead of Select case, if thenis used.

trim.bi

Code: Select all

'a low performance trimmer(maybe?)
#pragma once

'a simple lookup table for ASCII characters
dim shared as string trimset(255)
for i as short = 0 to 255
   trimset(i) = chr(i)
next

sub trimInStr(instring as string, byref outstring as string, trimchar as string)
   'clears outstring first
   outstring = ""
   'compare the string: if instring <> trimchar then copy the currently compared
   'character to the string
   for i as long = 0 to len(instring)-1
      if instring[i] <> trimchar[0] then : outstring += trimset(instring[i]) : end if
   next
end sub


Here's an example:

Code: Select all

#include "trim.bi"

dim as string outputstr
trimInStr("this is a test", outputstr, " ") ' trims spaces
print outputstr 'should print: "thisisatest"


[badidea]

Looks more complicated than it needs to be. Why the trimset and select case?
Same functionality:

Code: Select all

sub trimInStr(instring as string, byref outstring as string, trimchar as string)
   outstring = ""
   for i as long = 0 to len(instring)-1
      if instring[i] <> trimchar[0] then outstring += chr(instring[i])
   next
end sub

dim as string outputstr
trimInStr("this is a test", outputstr, " ") ' trims spaces
print outputstr 'should print: "thisisatest"


[dodicat]

outstring+=chr(instring[i])
is speeded up by the lookup table trimset.
(I assume this, I haven't tested)
but I agree, select case is not needed.
Here is another variety

Code: Select all

Function trimInStr(Byval TextIn As String,Char As String) As String
    dim as long ii,AC=Asc(char)
    For i As Long = 0 To Len(Textin)-1
        If Textin[i]<>AC Then Textin[ii]=Textin[i]:ii +=1
    Next
    Return Left(TextIn,ii)
End Function

dim as string outputstr
outputstr= trimInStr("this is a test"," ") ' trims spaces
print outputstr 'should print: "thisisatest"
sleep



[MrSwiss]

Even simpler: Function instead of Sub (direct result):

Code: Select all

Function trimInStr( _
    ByRef instring As Const String, _
    ByRef trimchar As Const String _
    ) As String
   Dim As String outstring = ""

   For i As UInteger = 0 To Len(instring) - 1   ' fastest up-counter (32/64)
      If instring[i] <> trimchar[0] Then outstring += Chr(instring[i])
   Next

   Function = outstring
End Function

' removes the stars ...
Print trimInStr("*greetings from *FreeBASIC*!", "*")
Sleep

[sancho3]

Mr.Swiss version with a few changes to make it even faster:

Code: Select all

Function trimInStr( _
   ByRef instring As Const String, _
   ByRef trimchar As Const String _
      ) As String
   dim as integer l = len(instring) - 1, n
   Dim As String outstring = space(l + 1)

   For i As UInteger = 0 To l
      If instring[i] <> trimchar[0] Then
         n += 1
         outstring[n] = instring[i]
      endif
   Next

   Function = trim(outstring)
End Function


[dodicat]

From my version 3 posts ago, compare:

Code: Select all


Function trimInStr( _
   ByRef instring As Const String, _
   ByRef trimchar As Const String _
      ) As String
   dim as integer l = len(instring) - 1, n
   Dim As String outstring = space(l + 1)

   For i As UInteger = 0 To l
      If instring[i] <> trimchar[0] Then
         n += 1
         outstring[n] = instring[i]
      endif
   Next

   Function = trim(outstring)
End Function

Function trimInStr2(Byval TextIn As String,Char As String) As String
    dim as long ii,AC=Asc(char)
    For i As Long = 0 To Len(Textin)-1
        If Textin[i]<>AC Then Textin[ii]=Textin[i]:ii +=1
    Next
    Return Left(TextIn,ii)
End Function


dim shared as string s:s=string(10000000,0)
for n as long=1 to 10000000
    s[n]=48+rnd*10
    if n mod 2=0 then s[n]=32
next
dim as string g=s
dim as long L
dim as double t
t=timer
 L=len(trimInstr(s," "))
print timer-t
print L
print



t=timer
 L=len(trimInstr2(g," "))
print timer-t
print L



sleep
 

[sancho3]

From my version 3 posts ago, compare:

Sorry dodicat, I didn't even pay attention to your version.
Its very similar to what I posted but a little faster.

[Takase]

outstring+=chr(instring[i])
is speeded up by the lookup table trimset.
(I assume this, I haven't tested)
but I agree, select case is not needed.
Here is another variety

Code: Select all

Function trimInStr(Byval TextIn As String,Char As String) As String
    dim as long ii,AC=Asc(char)
    For i As Long = 0 To Len(Textin)-1
        If Textin[i]<>AC Then Textin[ii]=Textin[i]:ii +=1
    Next
    Return Left(TextIn,ii)
End Function

dim as string outputstr
outputstr= trimInStr("this is a test"," ") ' trims spaces
print outputstr 'should print: "thisisatest"
sleep



yes. Trimset is for speeding up the overall speed as calling chr() everytime seems to slow down the program.

[Takase]

About the Select case , its my habit to use it instead of if else. Looks like my habit had got me. Thanks for all the replies tho! BTW, I did not do any DIMs in the sub because I'm afraid that it'll slow the sub down. So, can anyone tell me if DIMming the variables every call will decrease the performance or not? Will it bring a huge impact to the program speed?

[dodicat]

You have some choices for local variables.

Code: Select all


sub dothis
    dim as long a,b,c,d,e,f,g,h,i
    d=13
end sub

sub dothis2
    static as long a,b,c,d,e,f,g,h,i
    d=13
end sub


sub dothis3
    dim as long a=any
    dim as long b=any
    dim as long c=any
    dim as long d=any
    dim as long e=any
    dim as long f=any
    dim as long g=any
    dim as long h=any
    dim as long i=any
    d=13
end sub

dim as double t

t=timer
for n as long=1 to 1000000
    dothis
    next
    print timer-t
   
   
    print
    t=timer
for n as long=1 to 1000000
    dothis2
    next
    print timer-t
   
    print
     t=timer
for n as long=1 to 1000000
    dothis3
    next
    print timer-t
   
    sleep
     

[Tourist Trap]

I found a topic about trimming characters in a string in the forum before. But I've lost the link to the topic and I'm lazy to find it again. So, I wrote myself a little piece of code to trim a specified alphabet from a string.

yes there was a nice topic focused on performance in the General section, but I dont remember who started it. I guess you re talking about this one. From my part I did some general purpose stuff here below, dont know if it can help. No performance is targetted there:
viewtopic.php?f=7&t=25299&p=227595#p227595