module
6
Every time the compiler finishes, it prints seven lines of numbers and you have been ignoring them. They are worth a minute, because they answer three questions you will otherwise keep asking - what the compiler actually did, why a one-line program is ten thousand bytes, and why the disc is filling up so fast.
Compile the smallest program there is:
main()
{
}
0:HC EMPTY.C
HiSoft-C Compiler V1.35 Copyright (C) 1985
Line File
MEMORY MAP Start End
Runtimes 0100 11FF
Code 1200 1205
Initialisers 1206 1209
Fixed Data EC00 EC00
Smallest #data 0x1213
0:
Read it as a picture of memory, from 0100 upward, in hexadecimal.
main that does nothing: enough to begin and return.Everything between Smallest #data and Fixed Data is free for the program to use while it runs: the stack, where the variables of running functions live, and any memory it asks for (S21). In the empty program that is very nearly the whole machine.
Now S4's hello world:
Code 1200 1320
Initialisers 1321 1324
Fixed Data EBE3 EC00
Your one line of C has become 289 bytes of code, and Fixed Data has grown by 29. Most of that is not your line. Take both #include lines out of HELLO.C and compile it again and you get Code 1200 1224 - 36 bytes - and it still runs, because printf is built into the compiler (S8). The 250-odd bytes between are what STDIO.H and ?STDIO.LIB? bring in whether you use them or not: the library's own housekeeping.
That is cheap, and it is cheap because of the question marks. Write the last line as #include STDIO.LIB instead, with no ?, and put it at the top, and the map says Code 1200 250C: 4,876 bytes, the whole library compiled in, strlen and malloc and all the rest, whether you called them or not. With the ?, the compiler reads the library looking only for the functions your program has already used, and compiles those. Which is why the line goes last: anything called below it is not found.
So the numbers HC prints are worth a glance each time. A program that grows by a line grows by a few bytes; one that starts using a library function grows by that function.
0:DIR EMPTY.*
0: EMPTY .C : EMPTY .COM
8k Size, 64k Free, 190k Total
0:DIR HELLO.*
0: HELLO .C : HELLO .COM
8k Size, 64k Free, 190k Total
Every program is two files, and XtalDOS hands out disc space two kilobytes at a time, so even a three-line .C takes 2K. The .COM is the runtime plus the code, 6K for either of these - the 4,352 bytes of runtime are most of it, and the next 2K step is a long way off. (Hello world with the whole library compiled in, as above, is a 10K .COM and 12k Size.)
The course disc started with 72K free, which is nine programs or so; BREAKOUT.COM, the finished game, is on it already and is 10K of the rest. The .COM is the file to erase. You can make it again with one command; the .C is your work.
0:ERA HELLO.COM
0: HELLO .COM?
XtalDOS asks; press Y, and it says Erased. DIR HELLO.* now shows 2k Size and the 6K back in the free column.
One more thing about DIR. When the disc has more files than fit on the screen, DIR stops when the screen is full and waits for a key - and takes whatever you press as that key, including the first letter of the next command you were about to type. Press SPACE, wait for 0:, then type.
You can have the compiler show you every line as it reads it. Put #list+ on the command line before the file:
HC #list+ HELLO.C
The library's own source scrolls past first - STDIO.LIB opens with a comment giving its version, 1.3, and its date, 31 October 1985 - with a running line count that reaches 720, and then your eight lines, and then the map. The whole library goes past even though only the functions you used are compiled: ? decides what is compiled, not what is read. It is how you will read the library later (S23). Without #list+, only the names of the files go past, under Line File.
main()
{
}
Starting from
Typed as EMPTY.C and saved; HC EMPTY.C.
What you should see
The map above: Code 1200 1205 and Fixed Data EC00 EC00. Then EMPTY at the prompt runs it, and nothing at all happens, which is right.
#include lines to EMPTY.C and compile it again, still with nothing in main. How big is Code now, and what does that tell you about what the two lines cost?HELLO.C's last line to #include STDIO.LIB - no question marks. Compile it and look at Code and at DIR HELLO.*. Then put the question marks back.HELLO.COM, then type HELLO. What does XtalDOS say?DIR after each step of the cycle and watch the Size and Free numbers change.6.1 Using DIR, work out how many kilobytes of the course disc the compiler, the editor and the four library files take between them.
6.2 From the two maps above, say how many bytes hello world's Code is bigger than the empty program's, in decimal.
Worked solutions are in Appendix II.
| Symptom | Cause |
|---|---|
DIR stopped and the next command you typed has vanished | The pause took your first keystroke as "continue". Press SPACE at the pause and wait for the prompt. |
| The disc is full | Erase .COM files you do not need; the .C files make them again. |
#list+ scrolls too fast to read | It does. It is for counting, and for the reader's .LIB files, which S23 opens in the editor instead. |
The map is the program in memory: 4,352 bytes of runtime, then your code, then initialisers, with the top at Fixed Data. ?STDIO.LIB? compiles in only the library functions used above it; without the ? the whole library comes in. Each program is two files and 8K of disc; erase the .COM when you need room, and press SPACE when DIR pauses. #list+ shows every line the compiler reads.
S7, When It Goes Wrong - the compiler's error messages, the trick of pressing E, and the mistakes that produce no message at all.
