The printf statement is used to print text to the screen and lets you create markers in the text using the % char combined with another letter such as %i to show where the value of a specified vriable should be inserted in the text. In combination with the gotoxy() function (that positions the onscreen cursor), this is how most of the game's screen display is created. For more details on printf see this C tutorial.
- Read more about printf in C Tutorial on printf
However for some of the generated messages, it is necessary to first build up the string in memory and this is what the sprintf() function does. It's used in SendaMessage2 (shown below) and other places. Sprintf has one extra parameter at the start which is a string variable (in this case of type message). The output from sprintf goes into the string variable which can then be printed out using printf.
/* writes a message with a single int parameter */
void SendaMessage2(char * msgtext,int x) {
char buffer[100];
sprintf(buffer,"%s %i",msgtext,x) ;
SendaMessage(buffer) ;
}
If you are wondering why the first parameter uses a pointer (the * after a type means it's a pointer to that type), ie it's char * msgtxt and not message msgtxt, it's because message is fixed length and char * takes any length. Most of the time that won't matter but it is more flexible
Use of pointers as strings
In this tutorial, I'm not covering pointers (example char *) but they are used just as if they were strings. You will see a few string declaration that use pointers ie in SendaMessage/SendaMessage2 and other places, with declaration like this:
char * msgtext
But for now read this as being just like a string declaration, as if it was written
string message
Also in the GetInput function where the variable back is declared:
char * back ="\b \b";
again think of it as being like this:
string back ="\b \b";
When functions with a char * parameter are called, you can pass in a string in double quotes for example:
SendaMessage("You have captured ten systems") ;
Note:
The sprintf function is nowadays regarded as unsafe to use because it doesn't limit output. See this C tutorial on text file handling for more details about sprintf.
Special Control Chars
If you see a backslash followed by a single letter like \b, or \t \n \r \0 etc then these are special characters that don't print but affect the cursor or mark the end of a string (\0). The main ones are \b - backspace, \n and \r (carriage return and linefeed, usually used together to move the cursor down a line), \t (tab).
Conclusion
The next tutorial will look at the combat, computer AI etc in Star Empires.
