Starting with an empty file, can you write a complete C program to print out your favorite haiku poem, saying or famous CS quote?
Use 'write' system call to print your text.
Your main method should return an integer value zero (to mean it completed successfully).
Hint you'll need an #include and a 'main' function that returns an int.
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1.2 Hello Standard Error Stream
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Comments: In the video I say "C has no boolean type." That's a bit of a half-truth.
If you're using a more modern specification of C, C99 or newer, you can now #include stdbool.h
which includes a definition of a type 'bool' but it just
defines 'true' to be integer 1 and 'false' to be integer 0!
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Spot the mistake(s) in the following code
for(len = 0; len <5 ; len++) {
write(STDOUT_FNO,"I think", 6);
write(STDOUT_FILENUM,"\n", 6);
}
And use your corrected version in a complete C program to print the following seven lines.
Return the value 7. Verify that your program returns 7 typing "echo $?" in the terminal window after your program has just run.
Return the value 1023.
Why does "echo $?" in the terminal window after your program has just run not print 1023?
Hint: Some testing or web searching can tell you how many bits are actually used.
I think
I thin
I thi
I th
I t
I
I
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1.3 Writing to files
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Play
Part 1
Use your favorite search engine to find the man page for open (hint try "man open")
Can you create a program from scratch to create a file "message.txt", write a short message "hello!" and close the file handle.
Your text file should only be readable by you.
If you run your program again (e.g. "./program" in the terminal window)
Verify the contents of the file using "cat message.txt" in the terminal window.
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Part 2
Modify the program so that
Anyone can read your text file (hint which mode flag corresponds to "others have read permission")
Rather than truncate the file back to zero length each time, new text is appended to the end.
For example, running your program twice, and then "cat message.txt" you should see "hello!hello!"
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1.4 Not everything is a system call
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Send standard error to a file 'errors.txt' Hint: 'close' and 'open' are useful.
The file should always be truncated
Open another file with an illegal filename (e.g. "").
Use perror to send the error message to your log file.
Verify the contents of your log file using "cat errors.txt" in the terminal window.
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