Question

I wrote a C program. (Question at bottom of page) I can provide actual code, but I don’t think it is necessary for this question to be answered.

Used a while loop with fgets to get sizeof line
Assigned that fgets to line[255] in the fgets
Assigned the line to a char* (inside the loop)
Printf the char* (also inside the loop)

C program outputs as expected.

I used strace -o x.txt ./a.out to see what is going on behind the scenes.

I see this: (of course there is a lot more garble above/below it I don’t understand)

read(3, "text\nMore text\nEven more text"..., 4096) = 72
write(1, "text\n",5) = 5
... more of the write() = #
read(3, "", 4096) = 0
close(3)

Question:

1. I get the write(1=stdout, "text to print", #of char) or is this # of byte?

2. I do not understand the read(3, "", 4096) = 0

I know 0=stdin, 1=stdout, 2=stderr, do not know what 3 means – maybe this is the file?
I do not know why it is doing another read, and I assume 4096 is what the buffer size?
My best guess is that since it is saying = 0 because its EOF ?

Answer 1

1. Number of chars

2. The file you have opened. 4096 is buffer size. Last read has failed to read any bytes (0 bytes).