Programming Forums > Application Development > C++

Kilo · Jun 22nd, 2006, 9:43 PM

Ok the following code is being used to store an array of strings (being stored with memcpy). What is the * operater doing in the array declaration? I can't figure it out for the live of me! Is it just being used to declare 6000 elements?

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char G_cMsgList[120*50];

this is the routine used to store the Msg! I understand common things but certain thing like "cTemp + 120" is beyond me! Why would memcpy be used to store the msg's array (G_cMsgList) in cTemp them use memcpy again to store the new msg in cTemp and then take cTemp and put it in G_cMsgList again!

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void PutLogList(char * cMsg)
{
 char cTemp[120*50];
	
	G_cMsgUpdated = TRUE;
	ZeroMemory(cTemp, sizeof(cTemp));
	memcpy((cTemp + 120), G_cMsgList, 120*49);
	memcpy(cTemp, cMsg, strlen(cMsg));
	memcpy(G_cMsgList, cTemp, 120*50);

}

This is used to output the msg's (WM_PAINT). The main thing i don't understand is why the the declaration for a string is char * cMsg;.

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void OnPaint()
{
 HDC hdc;
 PAINTSTRUCT ps;
 register short i;
 char * cMsg;

	hdc = BeginPaint(G_hWnd, &ps);

	SetBkMode(hdc,TRANSPARENT);

	for (i = 0; i < 35; i++) {
		cMsg = (char *)(G_cMsgList + i*120);
		TextOut(hdc, 5, 5 + 600 - i*16, cMsg, strlen(cMsg));
	}

            	EndPaint(G_hWnd, &ps);

The reason for all of this is because im writting a text based rpg (still) using Win32 and I want to paint text (ofcourse). 1 first msg (line) being at the bottom of the window and each time i want to output a new msg (line) it is placed at the bottom and everything else shifts up a line. The code you see performs this action.. but i would never rip it. I want to completely understand how it was done before i attempt it (re-written). Thanks

bivhitscar · Jun 22nd, 2006, 10:05 PM

>Is it just being used to declare 6000 elements?

Yes.

And char * cMsg; is just a pointer to the text contained in the G_cMsgList array.

[EDIT]

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memcpy((cTemp + 120), G_cMsgList, 120*49);
memcpy(cTemp, cMsg, strlen(cMsg));
memcpy(G_cMsgList, cTemp, 120*50);

Copies the first 5880 elements in G_cMsgList into the cTemp array - starting from cTemp[120]. Then it copies the cMsg (current message?) into the start of cTemp. Now cTemp contains the new message, followed by the original first 49 entries in G_cMsgList. Then we copy that data back into the G_cMsgList array. So, basically, it just shifts the oldest message out and the newest message into the beginning of the array.

Kilo · Jun 22nd, 2006, 10:09 PM

but why char * cMsg why not char* cMsg or char *cMsg??? Or are they all the same?

bivhitscar · Jun 22nd, 2006, 10:16 PM

Yes, they are all the same.

nnxion · Jun 23rd, 2006, 8:19 AM

Btw it's written 'operator' not 'operater'.

Kilo · Jun 23rd, 2006, 10:18 AM

thanks nnxion i wrote these post last night after drinking a 6-pack. Anyone else have any insight about all of my other questions?

DaWei · Jun 23rd, 2006, 10:32 AM

It isn't a matter of insight. Which question did you ask that you didn't see an answer for?

Quote:

What is the * operater doing in the array declaration?

It's probably to remind the coder that the total number of elements declared represents a partitioning of m x n.

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	memcpy((cTemp + 120), G_cMsgList, 120*49);
	memcpy(cTemp, cMsg, strlen(cMsg));
	memcpy(G_cMsgList, cTemp, 120*50);

The first statement moves the message list into the temp area 120 bytes down from the beginning. The second statement moves cMessage to the beginning of the temp area (before the old message list). The third statement replaces the old message list with the new arrangement. This puts new messages at the front of the list, not at the rear. Capish?

Quote:

i don't understand is why the the declaration for a string is char * cMsg;.

As mentioned above, char *thangy, char* thangy, and char * thangy are equivalent.

Okay?

Cache · Jun 23rd, 2006, 12:06 PM

Perhaps part of the question is why use memcpy when C++ provide several abstractions for such operations. My anwser would be: I wouldn't. The code posted is probably written in C.

bivhitscar · Jun 24th, 2006, 3:57 AM

>Anyone else have any insight about all of my other questions?

I hate repeating DaWei, but what did you ask that I didn't answer?

Kilo · Jun 24th, 2006, 10:32 PM

I guess they were anwsered! lol sorry I had more then i didn't write... so i should be able to perform the same output using a (string) vector correct?

Jun 22nd, 2006, 9:43 PM	#1
Kilo Expert Programmer Join Date: Nov 2005 Location: In Pink Clam? Posts: 542 Rep Power: 0	operater and arrays Ok the following code is being used to store an array of strings (being stored with memcpy). What is the operater doing in the array declaration? I can't figure it out for the live of me! Is it just being used to declare 6000 elements? (Toggle Plain Text) char G_cMsgList[12050]; char G_cMsgList[12050]; this is the routine used to store the Msg! I understand common things but certain thing like "cTemp + 120" is beyond me! Why would memcpy be used to store the msg's array (G_cMsgList) in cTemp them use memcpy again to store the new msg in cTemp and then take cTemp and put it in G_cMsgList again! (Toggle Plain Text) void PutLogList(char * cMsg) { char cTemp[12050]; G_cMsgUpdated = TRUE; ZeroMemory(cTemp, sizeof(cTemp)); memcpy((cTemp + 120), G_cMsgList, 12049); memcpy(cTemp, cMsg, strlen(cMsg)); memcpy(G_cMsgList, cTemp, 12050); } void PutLogList(char cMsg) { char cTemp[12050]; G_cMsgUpdated = TRUE; ZeroMemory(cTemp, sizeof(cTemp)); memcpy((cTemp + 120), G_cMsgList, 12049); memcpy(cTemp, cMsg, strlen(cMsg)); memcpy(G_cMsgList, cTemp, 12050); } This is used to output the msg's (WM_PAINT). The main thing i don't understand is why the the declaration for a string is char cMsg;*. (Toggle Plain Text) void OnPaint() { HDC hdc; PAINTSTRUCT ps; register short i; char cMsg; hdc = BeginPaint(G_hWnd, &ps); SetBkMode(hdc,TRANSPARENT); for (i = 0; i < 35; i++) { cMsg = (char )(G_cMsgList + i120); TextOut(hdc, 5, 5 + 600 - i16, cMsg, strlen(cMsg)); } EndPaint(G_hWnd, &ps); void OnPaint() { HDC hdc; PAINTSTRUCT ps; register short i; char cMsg; hdc = BeginPaint(G_hWnd, &ps); SetBkMode(hdc,TRANSPARENT); for (i = 0; i < 35; i++) { cMsg = (char )(G_cMsgList + i120); TextOut(hdc, 5, 5 + 600 - i16, cMsg, strlen(cMsg)); } EndPaint(G_hWnd, &ps); The reason for all of this is because im writting a text based rpg (still) using Win32 and I want to paint text (ofcourse). 1 first msg (line) being at the bottom of the window and each time i want to output a new msg (line) it is placed at the bottom and everything else shifts up a line. The code you see performs this action.. but i would never rip it. I want to completely understand how it was done before i attempt it (re-written). Thanks __________________ "When in Rome, Do as the Romans Do" "Beauty is in the eye of the BEER* holder" "Save your breath your going to need it for your blow up doll later" SearchLores.org

Jun 22nd, 2006, 10:05 PM	#2
bivhitscar Hobbyist Programmer Join Date: Oct 2005 Location: Melbourne, Australia Posts: 126 Rep Power: 3	>Is it just being used to declare 6000 elements? Yes. And char * cMsg; is just a pointer to the text contained in the G_cMsgList array. [EDIT] (Toggle Plain Text) memcpy((cTemp + 120), G_cMsgList, 12049); memcpy(cTemp, cMsg, strlen(cMsg)); memcpy(G_cMsgList, cTemp, 12050); memcpy((cTemp + 120), G_cMsgList, 12049); memcpy(cTemp, cMsg, strlen(cMsg)); memcpy(G_cMsgList, cTemp, 12050); Copies the first 5880 elements in G_cMsgList into the cTemp array - starting from cTemp[120]. Then it copies the cMsg (current message?) into the start of cTemp. Now cTemp contains the new message, followed by the original first 49 entries in G_cMsgList. Then we copy that data back into the G_cMsgList array. So, basically, it just shifts the oldest message out and the newest message into the beginning of the array. __________________ it's ironic considerate rarity patron of love higher knowledge engulfs me... Last edited by bivhitscar; Jun 22nd, 2006 at 10:19 PM.

Jun 22nd, 2006, 10:09 PM	#3
Kilo Expert Programmer Join Date: Nov 2005 Location: In Pink Clam? Posts: 542 Rep Power: 0	but why *char cMsg why not char* cMsg or char cMsg??? Or are they all the same? __________________ "When in Rome, Do as the Romans Do" "Beauty is in the eye of the BEER* holder" "Save your breath your going to need it for your blow up doll later" SearchLores.org

Jun 22nd, 2006, 10:16 PM	#4
bivhitscar Hobbyist Programmer Join Date: Oct 2005 Location: Melbourne, Australia Posts: 126 Rep Power: 3	Yes, they are all the same. __________________ it's ironic considerate rarity patron of love higher knowledge engulfs me...

Jun 23rd, 2006, 8:19 AM	#5
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	Btw it's written 'operator' not 'operater'. __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

Jun 23rd, 2006, 10:18 AM	#6
Kilo Expert Programmer Join Date: Nov 2005 Location: In Pink Clam? Posts: 542 Rep Power: 0	thanks nnxion i wrote these post last night after drinking a 6-pack. Anyone else have any insight about all of my other questions? __________________ "When in Rome, Do as the Romans Do" "Beauty is in the eye of the BEER holder" "Save your breath your going to need it for your blow up doll later" SearchLores.org

Jun 23rd, 2006, 12:06 PM	#8
Cache Hobbyist Join Date: Sep 2005 Posts: 259 Rep Power: 3	Perhaps part of the question is why use memcpy when C++ provide several abstractions for such operations. My anwser would be: I wouldn't. The code posted is probably written in C.

Jun 24th, 2006, 3:57 AM	#9
bivhitscar Hobbyist Programmer Join Date: Oct 2005 Location: Melbourne, Australia Posts: 126 Rep Power: 3	>Anyone else have any insight about all of my other questions? I hate repeating DaWei, but what did you ask that I didn't answer? __________________ it's ironic considerate rarity patron of love higher knowledge engulfs me...

Jun 24th, 2006, 10:32 PM	#10
Kilo Expert Programmer Join Date: Nov 2005 Location: In Pink Clam? Posts: 542 Rep Power: 0	I guess they were anwsered! lol sorry I had more then i didn't write... so i should be able to perform the same output using a (string) vector correct? __________________ "When in Rome, Do as the Romans Do" "Beauty is in the eye of the BEER holder" "Save your breath your going to need it for your blow up doll later" SearchLores.org

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Programming Forums > Application Development > C++

*operater and arrays