Concat a Char to String.

[sergioms]

Hi,

How to Concat a Char to String? to add in the last position of array char...

void SendToPC (unsigned char *pMsg){
	
	unsigned char *cMsgFinal;
	int iLen;
	
	if (iUserSocket){

		cMsgFinal [0] = cInicio;
		strcat (cMsgFinal, pMsg);
		//cMsgFinal [0] = cFinal; ??????????????
		
		iLen = strlen (pMsg);
		
		VcomSendSocket(iUserSocket, pMsg, iLen);	
	}
}

[laserlight]

Um... but it looks like cMsgFinal is just a pointer that points to nowhere in particular. You certainly cannot concatenate anything to it.

[sergioms]

humm, and then

Whats the better option ?

[master5001]

void SendToPC (unsigned char *pMsg){
  if (iUserSocket)
  {
    size_t iLen = strlen (pMsg);

    pMsg[iLen] = cInicio;
    pMsg[iLen+1] = 0;
		
    VcomSendSocket(iUserSocket, pMsg, iLen);	
  }
}

[matsp]

Well, you'd definitely need to have some memory for cMsgFinal, either by allocating a sufficient size to hold the final string (don't forget to free it when you no longer need it), or simply declaring cMsgFinal as an array that can hold the length of the final string.

--
Mats

[laserlight]

Whats the better option ?

It depends on what are you trying to do. Your given code does not provide enough information: it is not clear what are cInicio and cFinal, or which string should be concatenated to which string, and in fact cMsgFinal looks completely redundant because it is not used.

[slingerland3g]

For arrays[] you must give the specific size that the array can possibly grow to be.

For pointers you must set aside memory for the object it will point to by using malloc and then free it when done.

[master5001]

Given that the parameter is not const I assume it is allowable for me to just be adding characters into it as opposed to making a second buffer. Though it makes no consideration for buffer overflow. But that is another issue altogether.

[sergioms]

void EnviaPedidoPC (unsigned char *pMsg){
	
	unsigned char cFinal [3];
	unsigned char *cMsgFinal;
	int iLen;
	
	if (iUserSocket){

		cMsgFinal [0] = cSTX;
		strcat (cMsgFinal, pMsg);
		cFinal [0] = cCR;
		cFinal [1] = cLF;
		cFinal [2] = '\0';
		strcat (cMsgFinal, cFinal);
		
		iLen = strlen (cMsgFinal);
		
		VcomSendSocket(iUserSocket, cMsgFinal, iLen);	
	}
}

[matsp]

cMsgFinal still points to "nowhere in partciular", which is not a good place to store things.

--
Mats

[sergioms]

ok, I will study Pointers

I'm not understand

[matsp]

ok, I will study Pointers

I'm not understand

Yes, it seems like you do not understand pointers. A pointer is essentially a variable that holds the address of something memory. Until you have set it to point to something, it doesn't "hold" any memory.

--
Mats

[Elysia]

http://cboard.cprogramming.com/showp...3&postcount=31

[master5001]

Bloody hell. What are you wanting to do, exactly?

void EnviaPedidoPC (unsigned char *pMsg){
	size_t iLen;
	unsigned char cFinal [3];
	unsigned char *cMsgFinal;

	if(!pMsg)
		return;

	if (iUserSocket){
		iLen = strlen (pMsg);
		cMsgFinal = malloc(iLen + 3);

		if(cMsgFinal)
		{
			//cMsgFinal[0] = cSTX;  <- what the f word is this?
			strcpy(cMsgFinal, pMsg);
			strcat (cMsgFinal, "\r\n");
			VcomSendSocket(iUserSocket, cMsgFinal, iLen);
			free(cMsgFinal);
		}
	}
}

[vart]

iLen = strlen (cMsgFinal);

Uh-oh! calling function on not-initialized pointer - just asking for crash