Code compiles etc. but just hangs on run - c

My program is meant to parse through a text file, extract relevant data and then save it in a SQL table. I compile it like so..
gcc -o parse parse.c -I/usr/include/mysql -L/usr/lib/mysql -lmysqlclient_r
then I run it like so...
./parse > tweets.rss
But it just hangs. it doesn't print any printf's I put in to debug. Whats wrong? here is my code...
http://pastebin.com/3R45zyMp
I'd appreciate any help!

You are specifying that it should write to tweets.rss instead of read from it. Since your program reads from STDIN as the first thing it does and you don't supply any input, why would you expect any output?
Try:
./parse < tweets.rss

The following is going to loop for ever.
while(c!= ' ' || c != '\t' || c != '\n' || c != '>'){
c = getchar(); //Get a new char
test[i] = c;
i++;
}
c can only be equal to one of them, so the condition will always be true.

Related

Why EOF(end of file) isn't working at the end of a line without a '\n' before it?

So I started to learn C using the ANSI C book. One of the early exercises in the book is to write a program that takes text input and prints every word on a new line, simple enough. So i did:
#include <stdio.h>
#define IN 1
#define OUT 0
main() {
int c;
int state;
state = OUT;
while((c = getchar()) != EOF){
if(c != ' ' && c != '\n' && c != '\t'){
state = IN;
}else if(state == IN){
state = OUT;
putchar('\n');
}
if(state == IN)
putchar(c);
}
getchar();
}
The thing is that while the program works fine it won't break from the while loop if I enter EOF(Ctrl+Z on windows) as the last char of a line or in the middle of it.
So I found an answer here.
What I learned is that the (Ctrl+Z) char is some sort of signal to end the stream and it must be on a new line for getchar() to return EOF. While this is all good and it kinda helped I really want to know why is it necessary for the EOF to be on its own line?
The problem you are having is related to your command line terminal and has nothing to do with the end of file marker itself. Instead of sending characters to the program as you type them, most terminals will wait until you finish a whole line before sending what you type to the program.
You can test this by having the input come from a text file instead of being typed by hand. You should be able to end the input file without a newline without any problems.
./myprogram.exe < input.txt
By the way, the answer you linked to also points out that EOF is not a character that is actually in your input stream, so there is no way for it to come "before" a "\n". EOF is just the value that getchar returns once there are no characters left to be read.
When reading from a tty device (such as stdin for a program running in a console or terminal window) the terminal is in so-called cooked mode. In this mode, some level of line editing facilities are provided, allowing the user to backspace and change what has been typed.
The characters that are typed are not returned to the program until after return has been pressed.
It is possible to do this by placing the terminal in 'raw' mode. Unfortunately it seems this is not well standardised though, so it is somewhat system specific. The answers to this question have some examples for various platforms.

Why does getchar() not work right?

Today, I wrote a simple piece of code that uses getchar() to count the characters you input. But when I compile it on Cygwin, it does not work. It always prints 0, but I never input anything or I can't input any characters it prints 0.
However, if I compile it with VC++6.0, it works.
#include<stdio.h>
int main(void)
{
long nc;
nc = 0;
while(getchar() != EOF)
++nc;
printf("The total of characters you inputed is %ld.\n", nc);
return 0;
}
This email thread talks about a bug that sounds much like yours, but I can't see that there are any follow-ups to it.
I would be interested to know what happened when you try
while(getc(stdin) != EOF)
and if that doesn't work, try
while(fgetc(stdin) != EOF)
All of them should work, though this page suggests there could be implementation differences between these functions.
Another thing you could try is to print the ASCII value of what you get:
printf("%d\n",(int)getchar());
Also, try piping output from a file instead of typing it in the console. Create a file input.txt, put some characters in it, and do
cat input.txt | ./program
EDIT: You write running cat and piping it works. I would say simply update your Cygwin version. You have encountered a bug. Get the newest versions of Cygwin and the compiler, and you should be good to go. Another option is to use scanf.

Program not printing out numbers

I'm a beginner in C and I bought the book "The C programming language" and started reading and doing everything it says. There is a code in the book which should print out the number of lines,words and characters of a sentence. This is the code of the book.
#include <stdio.h>
#define IN 1 /* inside a word */
#define OUT 0 /* outside a word */
/* count lines, words, and characters in input */
main()
{
int c, nl, nw, nc, state;
state = OUT;
nl = nw = nc = 0;
while ((c = getchar()) != EOF) {
++nc;
if (c == '\n')
++nl;
if (c == ' ' || c == '\n' || c = '\t')
state = OUT;
else if (state == OUT) {
state = IN;
++nw;
}
}
printf("%d %d %d\n", nl, nw, nc);
}
For some reason the values that should be printed out with the printf aren't shown. I really don't know what is wrong. It only prints out numbers if I put the printf in the while loop but this can't be right because it prints the numbers every time the values change.
You have a typo in this line -- the assignment of c = '\t' always evaluates to true
if (c == ' ' || c == '\n' || c = '\t')
To fix, change = to ==
if (c == ' ' || c == '\n' || c == '\t')
To answer your question why does it not print anything out -- I think that the compiler is either giving your an error or warning causing the program not being linked, and hence you are not actually compiling the source code as listed, but rather you are running an old version of whatever code you compiled before.
gcc gives a compile error on this line:
if (c == ' ' || c == '\n' || c = '\t')
looking # that line, it's easy to spot a typo: c = '\t')
missing an equality test, no?
:)
It looks like you are reading your input from STDIN (the keyboard) and leave the loop only on "End of file", which will not happen. Do as the other answer suggests.
Besides the typo others have mentioned, you need to send an End-Of-File signal to end the input loop. This will depend on the environment you are running it - will be Ctrl+Z in Windows, and should be Ctrl+D in *NIX environments. I needed to enter this on a new line and press Enter afterwards when using my usual IDE (Code::Blocks).
Remember too that at the time K&R (1 & 2) was written, command line programming was the norm, and typically you would expect the output to be visible if you just ended the program. Some IDEs will close their terminal emulator at the end of the program before you can view the results, so you may need to add something like
printf("\nPress return to continue");
getchar();
at the end of the program. Or, run it yourself from the OS terminal emulator (using cmd.exe on Windows, or gnome-terminal, yakuake, or whatever your OS provides). Navigate to the folder and
your_executable.exe
or
./your_executable
it was a equality issue as pointed above in if (c == ' ' || c == '\n' || c = '\t').
I would suggest you use a good IDE like Eclipse CDT which warns you of such bugs .

count blanks from the input

I wrote a program to count blanks. I can compile it and run it, it's fine. But why it does not display the count?
#include<stdio.h>
main()
{
int count=0;
int c;
while((c=getchar())!=EOF)
{
if(c == ' ') count++;
}
printf("%d\n",count);
}
Your exact code (errors and all) works as you'd expect at ideone.
How do you terminate the input? To send an EOF signal to your program from the console type, at the beginning of a line, CtrlD in Linux or CtrlZ in Windows.
Also try to run with redirected input. Something like
yourprog < data.txt
or
echo one two three four | yourprog
You're probably not getting the EOF that you expect from input. You may be expecting the Enter key to be EOF, which will not happen. Have you tried using one of the ctrl+ combinations such as Z or D (depending on OS) to send the EOF ?

Help With K&Rs Counting Chars Example

I'm working my way through K&R's 2nd edition, and I've been stumped with this seemingly simple example:
#include <stdio.h>
main(){
double c;
for(c = 0; ((getchar() != EOF) && (getchar() != '\n')); ++c)
;
printf("%.0f\n",c);
}
It simply isn't working correctly. I added in the (getchar() != '\n') portion to end the program when I press enter, but that doesn't really help either.
Here's some sample output, using the gcc that comes with Mac OSX 10.6 dev tools.
pool-000:Desktop user$ ./a.out
a
0
pool-000:Desktop user$ ./a.out
asdf
2
pool-000:Desktop user$ ./a.out
asfasf
3
So something is obviously wrong. I'm on page 18, if that helps. This isn't homework, this is for fun!
Thanks :)
Each call to getchar() will wait for a character to be read, so you're reading more than you think per iteration of the loop.
Also, at least in my opinion, a counter is (almost) never a double, you should use an integer type such as plain old int.
The problem with doing two "getchar()" operations is that you will read TWO get chars in the conditional test... before you get to the ++c.
Ditch the "EOF" comparison and it should work as you expect.

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