Help with WriteFile() api

[lochnessmonster]

i am currently using the writefile() windows api function in my program, i want to store the follow in 1 buffer but i'm unsure on how to do this exactly

"===================================" '\n'
	"Date: " localTime->tm_mon "/" localTime->tm_mday  "/" localTime->tm_year '\n'
	"Time: " localTime->tm_hour ":" localTime->tm_min  "." localTime->tm_sec '\n'
	 "===================================" '\n'
	 "[ERROR] - " ErrorString '\n'

i want to store it all in 1 buffer so i only have to do 1 call to writefile...i could have a buffer for each of the above segments for example

BYTE *buffer1 = "===================================;"
      BYTE *buffer2 = '\n';
      etc...

but i dont want to have to call consecutive called to writefile when i can only make one. Any advice is greatly appreciated! thx

[VernonDozier]

I'm unfamiliar with Windows programming, I've never seen the BYTE type, but presumably you can create a char* object containing everything and convert to a BYTE*, in which case you can use the standard cstring functions.

char buffer[100];
buffer[0] = 0; // not needed, but I tend to do it.
strcpy (buffer, "abcd");
strcat (buffer, "efgh");
strcat (buffer, "ijkl");

buffer now contains "abcdefghijkl". Use strlen to get the length. Typecast it and/or convert it to BYTE* and use your Windows function.

[caut_baia]

Or you can use stringstreams sort of like this

#include <string>
#include <sstream>
#include <iostream>
#include <windows>

int main ()  {
   std::stringstream format;
   format << "asd" << 5 << "gdfg\n";
   
   const char* to_write=format.str().c_str();   

   unsigned long readbytes;

   HANDLE hf=CreateFile ("asd.txt",GENERIC_READ|GENERIC_WRITE,
                          0,0,OPEN_ALWAYS,FILE_ATTRIBUTE_NORMAL,0);


   WriteFile (hf,to_write,format.str().size(),&readbytes,0);
 
 }

[caut_baia]

I'm replying to your private message here if you don't mind.I find it easier.If you want to code strictly in C you should go for the C string library as VernonDozier suggested.

[lochnessmonster]

template <class T>
void add_log(const T ErrorString)
{
	HANDLE hFileHandle;
	if( ( hFileHandle = CreateFile(L"log.txt", GENERIC_WRITE, 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL ) ) == INVALID_HANDLE_VALUE ) 
	 return; // throw GetLastError();

    SYSTEMTIME st;
    GetLocalTime(&st);

	std::wstringstream buffer;

	buffer << L"===================================\n" 
		   << L"Date: " << st.wMonth << L'/' << st.wDay    << L'/' << st.wYear   << L'\n'
		   << L"Time: " << st.wHour  << L':' << st.wMinute << L'.' << st.wSecond << L'\n'
		   << L"===================================\n" 
		   << L"[ERROR] - " << ErrorString << L'\n';

	const wchar_t* cStringBuffer = buffer.str().c_str();
 if(WriteFile( hFileHandle, &cStringBuffer, wcslen(cStringBuffer) , NULL, NULL ) == NULL )
  return;//throw GetLastError();

 
 CloseHandle( hFileHandle );
}

ok i did as you stated but for some reason the writefile api() is causing an access violation...and im not sure why? any ideas

[caut_baia]

Try replacing the NULL argument before the last with a valid address as i did.That's the argument that will receive the number of bytes written.

[maybnxtseasn]

thanks! it worked