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> Windows > Variable Length String |
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marcinzabrze12 13 Sep 2012, 19:01
run this code. It explain you wath is happend:
Code: include 'win32ax.inc' macro strcpy stra , strb { local label1 local label2 mov ecx,0 jmp label2 label1: inc ecx label2: mov al,[strb+ecx] mov [stra+ecx],al cmp [strb+ecx],0 jne label1 } .code start: strcpy str1 , str3 invoke MessageBox,HWND_DESKTOP,str2,invoke GetCommandLine,MB_OK strcpy str1 , str2 invoke MessageBox,HWND_DESKTOP,str1,invoke GetCommandLine,MB_OK invoke ExitProcess,0 .end start .data str1 db 'hello',0 str2 db 'harry',0 str3 db 'jupiter',0 beside i yor macro you use cmp [memory], value and mov ecx,0 change to cmp al,0 and xor ecx,ecx - it will be faster ps. why you jus not use lstrcpy function (WinApi) ? beside in assembly to text operation are specjal command: movs*, stos*, lods* .... they are faster and it is important because text operation are execute many times. Last edited by marcinzabrze12 on 13 Sep 2012, 19:09; edited 2 times in total |
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13 Sep 2012, 19:01 |
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typedef 13 Sep 2012, 19:03
You can make your macro strict, meaning it will fail if the destination address's length is less than the source's.
Or, you can just copy enough bytes that fit in the destination address. If the function is for versatile strings you can leave it as is otherwise you'd have to compensate for the null byte too. PS: Didn't mama teach you how to indent code ?  |
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13 Sep 2012, 19:03 |
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Masood.Sandking 13 Sep 2012, 19:18
thanks for answer...
'hello',0,'harry',0,'jupiter' => 'jupiter',0,'rry',0,'jupiter' => 'r',0,'rryer',0,'rry',0,'jupiter' it happens because last character of str1 is sticking to first character of str2. but what happens in high level programming languages like Basic or Pascal? how can i fix this problem? i heard something about dynamic memory allocation... do i need to do that? |
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13 Sep 2012, 19:18 |
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typedef 13 Sep 2012, 19:23
Another approach, but rather slow.
Code: macro strcpy [stra , strb] { local label1 local label2 push edi esi cld mov esi, strb mov edi, stra label1: lodsb cmp al, 0 je label2 stosb ; Or mov byte[edi], al / then inc edi jmp label1 label2: pop esi edi } |
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13 Sep 2012, 19:23 |
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Masood.Sandking 13 Sep 2012, 19:27
i'm not sure what is the lengths of those three strings at run time. i mean i don't want fixed-lenght strings... help me guys...
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13 Sep 2012, 19:27 |
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r22 13 Sep 2012, 19:49
HLLs use pointers to string objects.
Since you only have Copy you can do something a little simpler. Code: include 'win32ax.inc' macro strcpy stra , strb { MOV eax, [strb] MOV [stra], eax } .code start: strcpy pstr1 , pstr3 strcpy pstr1 , pstr2 invoke MessageBox,HWND_DESKTOP,[pstr1],invoke GetCommandLine,MB_OK invoke ExitProcess,0 .end start .data str1 db 'hello',0 str2 db 'harry',0 str3 db 'jupiter',0 pstr1 dd str1 pstr2 dd str2 pstr3 dd str3 |
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13 Sep 2012, 19:49 |
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typedef 13 Sep 2012, 20:00
This is more of a proc than a macro. I'm not a macro guru like revolution.
And this is not tested by the way. It's just to give you ideas. There might be bugs in it. Code: macro valloc [size]{ invoke VirtualAlloc, 0, size, MEM_RESERVER or MEM_COMMIT, PAGE_READWRITE } macro free [pointer]{ invoke VirtualFree, pointer, 0, MEM_RELEASE } ; ; Returns string length in eax ; macro strlen [string]{ local lbl_0 local lbl_1 push esi xor eax, eax cld mov esi, string lbl_0: lodsb cmp al, $00 je lbl_1 lea eax, [eax+1] jmp lbl_0 lbl_1: pop esi } macro strcpy [stra , strb] { local label1 local label2 local copy local strA_len local strB_len common strA_len = 0 strB_len = 0 push edi esi mov edi, stra push edi strlen stra mov dword[strA_len], eax strlen strb mov dword[strB_len], eax pop edi cmp dword[strA_len], eax ; destination jg copy mov eax, dword[strB_len] sub eax, dword[strA_len] add eax, dword[strB_len] valloc eax mov edi, eax xor eax, eax mov ecx, dword[strA_len] ; mov esi, stra ; for concatenation repnz stosb ; quick zero memory copy: mov esi, strb label1: lodsb cmp al, 0 je label2 stosb ; edi still points to the new address. jmp label2 label2: pop esi edi } Also shows you various ways of moving strings |
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13 Sep 2012, 20:00 |
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revolution 13 Sep 2012, 20:27
For most string related purposes using Virtual* functions is not a good choice. Consider using Heap* or Local* functions instead. They are a better fit for multiple small buffer allocations.
And remember that the Windows API has lstrcpy and related functions. You are reinventing the wheel if you write your own. |
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13 Sep 2012, 20:27 |
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AsmGuru62 14 Sep 2012, 02:05
I once took OlyDbg and traced lstrcpy - did not like it - too many strange calls into other stuff, probably for safety. I did my own CopyString.
Strings are fun to work with. When I was writing a parser - I noticed a pattern in string allocation. A lot of small strings must have been allocated in a loop and then freed. So, to improve it I allocated a big block (8 Mb) and put a pointer to the start of the block. Then when I needed some room - I simply moved pointer forward. At the end of loop, again moved it back to block start. I got almost twice speed-up against HeapAlloc. There is a danger of overwriting these 8 Mb on a huge file, but too huge files are impractical. Danger is there, however. |
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14 Sep 2012, 02:05 |
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typedef 14 Sep 2012, 03:35
AsmGuru62 wrote: Strings are fun to work with. This sounds like a good idea. I have to try it out in my app. So basically it's like a "workplace" for manipulating strings. Thanks for this idea. I think it will fit with my app since the strings I'll be handling are not above 5KB. Maybe 2 MB will work. But I'll see. |
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14 Sep 2012, 03:35 |
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Jimmus 14 Sep 2012, 15:38
You could assign an arbitrary max, and use that
Code: str1 db 'hello',0 rb 20 str2 db 'harry',0 str3 db 'jupiter',0 |
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14 Sep 2012, 15:38 |
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Masood.Sandking 19 Sep 2012, 20:15
I prefer dynamic allocation... But i have never done it before... Is there any simple example specially for working with strings? Or any useful example to understand HeapAlloc...?
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19 Sep 2012, 20:15 |
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rohagymeg 23 Sep 2012, 17:07
Memory management in windows works like this:
Program memory is divided into heaps. There is a default heap for every process, so if your program is simple, you don't need to create any heap at all: Code: invoke GetProcessHeap;Returns the handle of the main heap. invoke HeapAlloc, eax, HEAP_ZERO_MEMORY, 100 There you have it. HeapAlloc gets process heap handle in eax, HEAP_ZERO_MEMORY guarantees that all the bytes are 0. And the last parameter is what you wanted to know. Just as for any other function, you can pass a constant, register, or memory offset. The size is in bytes. If someone writes a large program that needs memory allocation and deallocation, it's essential to have multiple heaps, because you can free them if you don't need them. This is when HeapCreate comes into play: Code: invoke HeapCreate, HEAP_GENERATE_EXCEPTIONS, 0, 0 mov [MyMem], eax invoke HeapAlloc, eax, HEAP_ZERO_MEMORY, 100 mov [MyAlloc], eax ;After you called HeapAlloc, you can no longer use it for that heap. HeapReAlloc should be used: invoke HeapReAlloc, [MyMem], HEAP_GENERATE_EXCEPTIONS+HEAP_ZERO_MEMORY, eax, 200;Allocation properties are changed ;To access your memory, the best way is to load the address into a register: mov ebx, [MyAlloc];The pointer of the first byte is loaded into ebx mov dword [ebx], "Test" add ebx, 4;Now ebx points to the zero byte which is after "Test" mov word [ebx], "in" add ebx, 2 mov byte [ebx], "g" ;If you want to write more: inc ebx;So on... ;If you no longer need the heap, just call HeapFree invoke HeapFree, [MyMem], 0, [MyAlloc] It's not my job to explain what msdn explains. And even if I did, I couldn't explain it clearer than msdn. Please look up these functions to understand the parameters. Hope I helped
EDIT: I didn't try, but if you are able to call HeapAlloc more than once on a heap without getting appcrash, then it's completely legal to use, but your data on the heap will be lost. HeapReAlloc can change the heap properties, like increasing/decreasing size, without losing the data. Unless you give less size than your data is. |
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23 Sep 2012, 17:07 |
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