Search for string in memory block

[GS611]

I did a pretty thorough search for this but didnt come up with anything but strstr and memchr functions. I am trying to search for a 4 byte string in a memory area created with GlobalAlloc and ReadFile.

I created a function with two parameter for a pointer to memory and size. In my loop I'm getting conversion errors of char * to char[4] and such. I also type casted the FileSize as int to get rid of erros with conversions to int since that is what I want to do (I think).

int FindPOL2(char *lpBuffer, LPDWORD FileSize) {
	char POL2[4] = {'P','O','L','2'};
	char buffer[4];
	for (int i=0; i<=(int)FileSize-4;i++){
		if (*(lpBuffer+i) == POL2){
			return i;
		}
	}
	return -1;
}

My real question is: since buffer[4] is 4 bytes, why doesn't *(lpBuffer+i) return just 4 bytes? Or am I going to have to do lstrcmp here?
Albeit longer, this in assembly is so much easier.

[PanGalactic]

What you are writing here is not C++, but Microsoft-specific C code.

Why not use std::ifstream, std::istream_iterator and std::search?

[Galik]

Is this what you are looking for?

#include <cstring>
#include <algorithm>

const int SIZE = 1024;

int main()
{
	char* data = new char[SIZE];

	data[24] = 'P';
	data[25] = 'O';
	data[26] = 'L';
	data[27] = '2';

	const char* POL2 = "POL2";

	char* found = std::search(data, data + SIZE, POL2, POL2 + strlen(POL2));

	if(found < data + SIZE)
	{
		std::cout << "found: " << found - data << '\n';
	}

	delete[] data;
}

[Galik]

Or as a nice neat function:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

/** * Find string 'str' in data buffer 'buf' of length 'len'. * * @return size_t offset or len if not found. */ inline size_t offset(const char* buf, size_t len, const char* str) { return std::search(buf, buf + len, str, str + strlen(str)) - buf; } int main() { char* data = new char[1024]; data[24] = 'P'; data[25] = 'O'; data[26] = 'L'; data[27] = '2'; size_t o = offset(data, 1024, "POL2"); if(o < 1024) { std::cout << "found: " << o << '\n'; } }

found: 24

[jsmith]

If copying the source isn't a performance problem then

std::string( buf, len ).find( "POL2" ) != string::npos

works.

[GS611]

PanGalactic: Thanks for the info about what I was writing. Most of my "c++" knowledge has been from looking at others examples. I though that was more or less a standard way to do things with pointers.

jsmith: eventually the buffer is going to be at least a megabyte in size with multiple POL2 sections. And I didn't want to use string library because from what I can tell it will stop at the first Null byte it finds (or is that specifically C strings?)

Galik: Thanks for that code snipplet, I found the search function in the Cstring.h file. I'll test this out later today.

[Galik]

Only cstrings are null terminated. std::string can contain nulls as normal values. Also the std::search() function is in the <algorithms> header. I included <cstring> to get strlen();