Thread: Best method to alloc memory for string and desalloc.

Code:

char *
     strncpy(char *restrict s1, const char *restrict s2, size_t n);

The strncpy() function copies at most n characters from s2 into s1. If
s2 is less than n characters long, the remainder of s1 is filled with
`\0' characters. Otherwise, s1 is not terminated.

From:
http://www.manpagez.com/man/3/strncpy/
(My bold)

--
Mats

If s2 is less than n characters long, the remainder of s1 is filled with
`\0' characters. Otherwise, s1 is not terminated.

Oops! My mistake. Sorry. Thanks matsp. I'll edit my last post...

Originally Posted by sergioms

in this case,
[...]
yes?

No. strlen looks for the \0, so there is never a point in doing that. If strncpy did not add a null terminator, then strlen will give an incorrect result.

Of course, you could always just provide an extra character so that strncpy will add a \0.

Code:

substring(&string[11],sub,7);		
substring(&string[5],sub2,6);

Code:

void substring (char *string, char *substr, int numchars) {
	strncpy(substr,string,numchars);
        substr[numchars+1]='\0';
}

This is MK27's corrected code - I'm not sure if you should have the +1 there or not - I think not. But either way, something like that is correct.

--
Mats

Originally Posted by sergioms

in this case, the function always copy +1 char,

Yep. Which means that other version of mine would cause the same problem. So you do have to add a null terminator in that function.

Code:

                iPosStart = strpos (pPacote, cSTX);
	iPosStart++;
	
	iPosEnd = strpos (pPacote, cCR);
	
	iPosTam = iPosEnd - iPosStart;
	

	if((iPosStart >= 0) && (iPosEnd)){
		substring(&pPacote[iPosStart], cPacote, iPosTam);

		VcomSendSocket(iUserSocket, cPacote, strlen (cPacote));
	
		if(strlen (cPacote) > 0){
						

			substring(&cPacote[0], cFuncao, 2);

			VcomSendSocket(iUserSocket, cFuncao, strlen (cFuncao));
			
			if (strcmp (cFuncao, "OP") == 0){								// Recebe Ordem de Pesagem
								substring(&cPacote[3], cSubFuncao, iPosTam - 2);
								VcomSendSocket(iUserSocket, cSubFuncao, strlen (cSubFuncao));
				OrdemProducao (cSubFuncao);

pPacote: OP F04 686693 1 BL1 MASSA MONOPOROS

Output (VcomSendSocket):

6/1/2009 09:39:16 - Rec: PASSO 1[NULL]
6/1/2009 09:39:16 - Rec: CC F04 686693 1 BL1 MASSA MONOPOROS�PASSO 2CC�[NULL]

i want to get only the middle string without null and others chars.

:S

like my old function:

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;
}

Code:

void substring (char *string, char *substr, int numchars) {
	strncpy(substr,string,numchars);
        substr[numchars+1]='\0';
}

should work, but I still think that if numchars is the actual number of characters you want to copy [which I think it should be], then you should set the zero to indicate the end at [numchars], not [numchars+1], since C arrays start at zero, and [numchars] really is the (numchars+1)th element - e.g. if we have a length of 2, then [2] is the third element of the array.

--
Mats

Originally Posted by sergioms

There is someone command to clear all allocated memory ?

You mean "free everything", - no there is no such thing - you couldn't meaningfully make use of such a function anyways, because it would require that no functions that you ever call to the C library or such uses malloc - which they may possibly do.

--
Mats

unsigned or signed char should only make a difference if you are:
1. comparing (unsigned has no negative values, so all characters are in a uniform range 0..255, whilst characters that are above 127 become negative values in signed form).
2. When converting to (signed) integer - an unsigned will retain the same 0..255 value, whilst the signed char will give a value -128..127.

You certainly do not need to allocate space for all strings - you only need to allocate space if you:
1. Use A LOT of space (several kilobytes or more)
2. Do not know how much space you need, and the largest amount is VERY large compared to the smallest amount [particularly if you have many strings and want to conserve space].

Using

Code:

char str[SIZE];

will create a string of SIZE elements, which should work for cases where SIZE can be determined before you run the program - and as long as the largest size you need is less than (say) a few hundred bytes, it's the best way to get space for a string.

--
Mats