Analizing characters in a String

[atreiooo]

Hello to All,
Sorry for my trivial question, but i' m a beginner in programming.
I'm working around a long printable string and i have to find some particular substring composed only by numbers "0..9", characters "A...Z" or "a...z" and not any other characters.
Could someone suggests which is the best way to do that?
Thanks. Enrico

[Gonzo]

int position = instr(string, "search")

http://www.freebasic.net/wiki/wikka.php ... KeyPgInstr

[counting_pine]

Unfortunately instr only allows you to search for an exact match. You can do something like this though:

Code: Select all

function isalphanum(byval char as integer) as integer
 '' return -1 for char alphanumeric, 0 otherwise

 select case as const char
 case asc("0") to asc("9"), asc("A") to asc("Z"), asc("a") to asc("z")
  return -1
 end select

 return 0

end function


function scanfor(byref s as const string, byval start as integer = 1, byref length as integer = 0) as integer
 '' scan s for alphanumeric string, return length in third parameter

 dim as integer i = start, n = len(s)

 do
  if i > n then return 0
  if isalphanum(asc(s, i)) then exit do
  i += 1
 loop

 start = i

 do
  if i > n then exit do
  if not isalphanum(asc(s, i)) then exit do
  i += 1
 loop

 length = start - i + 1
 return start
 
end function

[srvaldez]

an elegant solution counting_pine, but for a beginner it might be frightening complex, here's a very simplistic approach.

Code: Select all

dim as string mask = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmopqrstuvwxyz"
dim as string st = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ.abcdefghijklmopqrstuvwxyz"
dim as integer i

for i=1 to len(st)
    if instr(mask,mid(st,i,1))=0 then
        print "found "+""""+mid(st,i,1)+""" at position ";i
    end if
next

sleep

[counting_pine]

If you don't want to find the length of the substring, then you could find the first matching character with something like:
instr([start,] s, any "0...9A...Za...z")

(The 'any' string is truncated for readability, not using fancy regular expressions or anything; it would look like the mask in srvaldez's code.)

[srvaldez]

good tip counting_pine :)

[atreiooo]

I thank all that helped, Enrico

[atreiooo]

It's me again with a smal question, but hard for me.
When i save my string in a file (and i use : Write #f, my-string), in the file i find a " " " (quotation mark) as the very first and the last character.
The quotation mark is not present in the string and i think it is the write operation to generate them.
How can i avoid that noisy insertion?
Thanks for your replay.
Enrico

[Mihail_B]

It's me again with a smal question, but hard for me.
When i save my string in a file (and i use : Write #f, my-string), in the file i find a " " " (quotation mark) as the very first and the last character.
The quotation mark is not present in the string and i think it is the write operation to generate them.
How can i avoid that noisy insertion?
Thanks for your replay.
Enrico

Instead of "write" use "print"

Code: Select all

dim as string a
dim as string b

a= "hello file world"

open "Readme222.txt" for output as #1
print #1,a 
print #1,a;" <-second"
close #1

open "readme222.txt" for input as #1
line input #1,b
print b
line input #1,b
print b
close #1
sleep

to print a text file until it ends you can do this :

Code: Select all

dim as string a,filename

line input "Filename (and path):",filename
if filename="" then 
  print "no file"
  beep
   end
endif


open filename for input as #1
while not eof(1)
  line input #1,a
  print a
wend
close #1
sleep

[atreiooo]

Mihail_B, i thank you very mutch
Enrico

[thrive4]

Riffing on the code of counting_pine

Code: Select all

' check if string contains alphanumeric value
' courtesy counting_pine https://www.freebasic.net/forum/viewtopic.php?p=166250&hilit=isalphanum#p166250 
function isalphanumeric(haystack as string) as boolean
    dim i as integer
    do
        select case asc(mid(haystack, i, 1))
            case asc("0") to asc("9"), asc("A") to asc("Z"), asc("a") to asc("z")
            return true
        end select
        i += 1
    loop until i > len(haystack)

    return false

end function

[UEZ]

I would suggest learning regular expressions for this kind of task. I know it's not easy to learn, but you can more easily perform complex string operations.

Example:

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#Include "pcre.bi"

Function RegEx(Byval aPattern As String, Byval aSubject As String, aArr() As String) As Integer
  Const OVECCOUNT = 300
  
  Dim As Zstring Ptr error_
  Dim As Long error_offset, rc, i, ovector(OVECCOUNT - 1), result
  Dim As pcre Ptr re
  
  Erase aArr
  result = 0
  
  re = pcre_compile(aPattern, 0, @error_, @error_offset, NULL)
  If re = NULL Then
    Return result
  End If
  
  i = 0
  Do
    rc = pcre_exec(re, NULL, Strptr(aSubject), Len(aSubject), i, 0, @ovector(0), OVECCOUNT)
    If rc > 0 Then
      Redim Preserve aArr(Lbound(aArr) To Ubound(aArr) + 1)
      aArr(Ubound(aArr)) = Mid(aSubject, ovector(0) + 1, ovector(1) - ovector(0))
      result += 1
      i = ovector(1)
    End If
  Loop While rc >= 0

  Return result
End Function

Sub PrintArray(aArr() As String)
  For i As Integer = Lbound(aArr) To Ubound(aArr)
    Print(Trim(aArr(i), Any Chr(10, 13, 32)))
  Next i
End Sub


Dim As String aResult(), sPathWindows, sPathLinux

sPathWindows = "c:\Windows\System32\catroot\{127D0A1D-4EF2-11D1-8608-00C04FC295EE}\Test.txt"
RegEx("[A-Za-z0-9]+", sPathWindows, aResult())
PrintArray(aResult())
Sleep

This will extract the words from the string according your criteria and output should be:

Code: Select all

c
Windows
System32
catroot
127D0A1D
4EF2
11D1
8608
00C04FC295EE
Test
txt

If you need libpcre.a you can download it from here: viewtopic.php?f=17&t=19095&start=495#p278794