Mid function in C

This is a discussion on Mid function in C within the C Programming forums, part of the General Programming Boards category; Code: char *substr(const char *pstr, int start, int numchars) { char *pnew = malloc(numchars+1); strncpy(pnew, pstr + start, numchars); pnew[numchars] ...

  1. #1
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    Mid function in C

    Code:
    char *substr(const char *pstr, int start, int numchars) 
    {
    	char *pnew = malloc(numchars+1);
    	
    	strncpy(pnew, pstr + start, numchars);
    	pnew[numchars] = '\0';
    	return pnew;
    }
    
    int strrpos (unsigned char *pStrText, char pChar){	// Última ocorrência do caractere.
    	
    	int iLen, iCont;
    	iLen = strlen (pStrText);
    
    	if (iLen > 0){
    		for (iCont=iLen - 1; iCont>=0; iCont--){
    			if (pStrText[iCont] ==  pChar)
    				return iCont;
    		}
    		return 0;	// Não houve ocorrências
    	}
    	else { return 0; }	// String Nula
    }
    
    int ProcessaChamado (char *pPacote, int pLen){
    	
    	char *cTeste = malloc (30);
    	char *cFuncao;
    	char *cPacote = malloc(pLen);
    	
    	int iPosStart, iPosEnd, iPosTam;
    			
    	//Separa o Pacote
    	iPosStart = strrpos (pPacote, cSTX);
    	if(iPosStart >= 0) 
    		iPosStart++;
    	
    	iPosEnd = strrpos (pPacote, cCR);
    	
    	iPosTam = iPosEnd - iPosStart;
    		
    	if((iPosStart) && (iPosEnd)){
    		cPacote = substr(pPacote, iPosStart, iPosTam);
    	} 
    	else { return 0; }
    	
    	if(strlen (cPacote) > 0){
    		
    		cFuncao = substr (cPacote, 0, 2);
    		
    		sprintf (cTeste, "%s %s %c %c %d", cFuncao, cPacote, cFuncao[0], cFuncao[1], strlen(cFuncao));
    		printCom1 ("TESTE: %s\n", cTeste);	
    		
    		if (strcmp (cFuncao, "OP") == 0)
    			printCom1 ("OK!");
    		
    	} 
    	else { return 0; }
    	
    	return 1;
    }
    I need got the XX (pos 1 e 2 of string) in send string

    Send: XX34567890AB

    Received: X3 X34567890AB X 3 2

  2. #2
    Resu Deretsiger Nightowl's Avatar
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    Umm . . . alright. I don't fully understand what you mean.

    Could you try to post some more information on what you're trying to do here?

  3. #3
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    the substr function, is similliar to function MID to get char at a position in a string.

    In function ProcessaChamado , I Send [2]XX34567890AB[13][10], and your length

    when I call cFuncao = substr (cPacote, 0, 2);

    I Need Get XX of sended package.

    Obs: cPacote is XX34567890AB without 2 13 10 char.

  4. #4
    Resu Deretsiger Nightowl's Avatar
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    I'm trying to understand what you mean. Tell me if I'm understanding you correctly.

    The substr() function returns a small section of a string in a new string, standard stuff.

    In the function ProcessaChamado, you pass it a string and a length . . . according to the prototype.

    What exactly, do you mean by "I Need Get XX of sended package"? Do you mean that you need to get the length of the original string? Or get the first two characters?

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    get the first two characters

    sorry for my english guy

    im brazilian!

  6. #6
    Resu Deretsiger Nightowl's Avatar
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    Oh, that's it . . . sorry. No, just remember that you should elaborate on what you mean, and we'll understand you much better.

    Code:
     . . .
    if(strlen (cPacote) > 0) {	
        cFuncao = substr (cPacote, 0, 2);
     . . .
    Are you not getting the first two characters there? (BTW, you should check if the string is longer than 2 chars, not 1. Otherwise you could end up trying to get the first two characters of a 1-character string.)

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    Sorry I don't undestand,
    I'm confused

  8. #8
    Resu Deretsiger Nightowl's Avatar
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    Does that code segment not give you the first two characters in the string cPacote?

  9. #9
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    yes, segment give second and third characters in the string cPacote.

  10. #10
    Resu Deretsiger Nightowl's Avatar
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    . . . so just use something similar for pPacote?

  11. #11
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    pPacote is [2]XX34567890AB[13][10] is ok!

    cPacote is X34567890AB

    But Im Call Function in cPacote = substr(pPacote, iPosStart, iPosTam);

    Where iPosStart = 1 iPosTam = 11

    And corretly return of cPacote need be XX34567890AB
    and not [2]X34567890AB

  12. #12
    Frequently Quite Prolix dwks's Avatar
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    Are you saying that the return value of substr() is not as you expect? It seems okay to me; it extracts a string starting at the given position with the given length. For example, "Hello" starting at 1 with length 2 would be "el".

    Note that the last parameter to substr is a length, not an index.

    I too am not sure what you are asking. What is "[2]X34567890AB"?
    dwk

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    [2]X34567890AB is the returned string of substr function.

    but,

    I Need this XX34567890AB

  14. #14
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    If I got it then a lot depends on what strrpos() looks like and the arguments you are passing to it cCR and cSTX. So if you could tell some more about it, that would be helpful.

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    iPosStart = strrpos (pPacote, cSTX);

    if(iPosStart >= 0)
    iPosStart++;

    iPosEnd = strrpos (pPacote, cCR);

    iPosTam = iPosEnd - iPosStart;

    Result:

    cPacote: XX34567890AB
    pPacote: X34567890AB
    iPosStart/iPosEnd/iPosTam: 1 12 11

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