Your char* is uninitialised and not pointing at a chunk of memory you can write to. You can either use new or malloc() to dynamically allocate some memory, or you can use an array, or the best option, swop the char* for a std::string
char* fileTxt = new char;
The string option is best as the memory managment is done for you by the string class. I used 256 as an example size, but im sure you get the idea. Remember malloc must be matched with a free(), new matched with a delete. The array is made on the stack so no special cleanup needed for that.
Get Microsoft Visual C++ Express here or CodeBlocks here.
Get STLFilt here to radically improve error messages when using the STL.
Get these two can't live without C++ libraries, BOOST here and Loki here.
Check your code with the Comeau Compiler and FlexeLint for standards compliance and some subtle errors.
Always use [code] code tags [/code] to make code legible and preserve indentation.
Do not ask for help writing destructive software such as viruses, gamehacks, keyloggers and the suchlike.