Thanks Don!
Yes, I tried your code of post #2, which worked of course. Before my post I tried this version for format2.dat as I thought C takes input by line:
both of which worked, but look very weird even to myself! Along with your version, I have three ways to do the same thing! These give me confusion that brought my post.
Book and tutorials I read use format1.dat as example to fill struct. From the manpage, it is not very clear to me without an exact example:
Code:
A sequence of white-space characters (space, tab, newline, etc.; see isspace(3)). This directive matches any amount of white space, including none, in the input.
Handling stream (including parsing) in C is quite challenging to me, it is better now with fscanf(). Thanks a lot again!
The %s is changed to something that won't stop at the first whitespace, %[^\r\n] will accept all text up to but not including newlines.
...except this is dangerous. There's no way to prevent buffer overruns or do error checking and it will choke at the first mistake in your input. Don't use fscanf. Use fgets and sscanf like I keep telling you.
Last edited by Corona688; 04-08-2015 at 01:03 PM..
How scanf/fscanf/sscanf work is it scans a string and stops whenever the input doesn't match what you've specified or it finds whitespace. It's kind of like a regex -- you're creating a string which matches the data you want, with various kinds of wildcards. But it's very different from a regex in that it doesn't stop at the end of the line, it stops wherever it pleases. You can force it with %[charstoaccept] / %[^charstonotaccept], a %s-equivalent I first saw in a config file loader which suddenly had to cope with carriage returns when ported to Windows. (And people wonder why I'm paranoid about those.)
Suppose you're scanning
Code:
abcde 3.14159
c d e
with %s %lf %s. It starts with %s, and accepts 'a', 'b', 'c', 'd', 'e' into the string. Then it sees whitespace and decides the string is over.
The space betweeh %s and %lf tells it "whitespace is acceptable", so it skips past the whitespace.
After that, it gets to %lf, scans '3', '.', '1', '4', '1', '5', '9', and processes that into a float, then hits \n which tells it the number's now over.
The space between %lf and %s tells it whitespace is acceptable. So it skips past all three newlines and starts reading 'c' into a string, and stops immediately because it's hit some whitespace. Since it's completely finished the command string "%s %lf %s", it feels no need to do anything with that whitespace and leaves it there for next time.
...Which means, the next time you scan "%s %lf %s", it will quit immediately because %s sees a white space and stops. The point is, fscanf leaves the file things in an unpredictable place unless things go exactly as planned.
This is why I always read entire lines. sscanf() can't choke and leave stdin in a weird place, because the entire line has already been read. If you want sscanf to read several entire lines, it can do that too.
Code:
#include <stdio.h>
#include <string.h>
typedef struct abc {
char a[64], b[64], c[64];
} abc;
int main(void)
{
char buf[4096];
abc a;
while(!feof(stdin)) {
int bpos=0;
// Read three lines into the same buffer.
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
bpos = strlen(buf); // could be more efficient but you get the idea
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
bpos = strlen(buf);
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
sscanf(buf, "%[^\r\n] %[^\r\n] %[^\r\n]", a.a, a.b, a.c);
printf("a: %s\nb: %s\nc: %s\n", a.a, a.b, a.c);
}
}
Code:
$ printf "a b c\nd e f\ng h i\n" | ./a.out
a: a b c
b: d e f
c: g h i
$
Last edited by Corona688; 04-08-2015 at 01:34 PM..
is dangerous in many ways, doesn't do precisely what you want(%s stops at first whitespace) and has no good options for error-checking.
A solid understanding of the functions fscanf(), sscanf(), fgets() is needed to use them properly. Use fgets and sscanf like I keep telling youI was trying to understand why, and before that, I need catch how "flow of the data" (sometime I think it as stream) was read into memory, or handled by the program. RS/FS was borrowed to show my understanding as awk handle formatted data with these two VAR, which is not appropriate here apparently. So many options, I need understand the right choice. This part is hard at my first sight to Read three lines into the same buffer
Code:
// Read three lines into the same buffer.
if(!fgets(buf, 4096-bpos, stdin)) break; //To help my understanding, can I do this, as bpos is set 0 before the loop?
bpos = strlen(buf); // could be more efficient but you get the idea
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
bpos = strlen(buf);
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
I'm sorry, I've been editing my posts a lot. I've now included an explanation of exactly what fgets does and why it's so annoying -- it might read halfway through a line and stop there.
// Read three lines into the same buffer.
if(!fgets(buf, 4096-bpos, stdin)) break; //To help my understanding, can I do this, as bpos is set 0 before the loop?
bpos = strlen(buf); // could be more efficient but you get the idea
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
bpos = strlen(buf);
if(!fgets(buf+bpos, 4096-bpos, stdin)) break;
Yes, you can. I have 3 lines exactly the same because I was going to put them into a loop, but didn't, to make it clearer.
We have the data looks like below in a log file.
I want to generat files based on the string between two hash(#) symbol like below
Source:
#ext1#test1.tale2 drop
#ext1#test11.tale21 drop
#ext1#test123.tale21 drop
#ext2#test1.tale21 drop
#ext2#test12.tale21 drop
#ext3#test11.tale21 drop... (5 Replies)
Hi,
I have below data in my flat file.I would like to remove the quotes and comma necessary from the data.Below is the details I would like to have in my output.
Could anybody help me providing the Unix shell script for this.
Input :
ABC,ABC,10/15/2012,"47,936,164.567 ","1,036,997.453... (2 Replies)
I have this input.|user1 |10.10.10.10 |23|046|1726 (212) |0
|user2 |10.10.10.11 |23|046|43 (17) |0
|test |10.10.10.12 |23|046|45 (10) |0
|test1 |10.10.10.13 |23|046|89 (32) |0
I need to get the data for a user like thisuser1 1726
user2 43
test 45
test1 89... (11 Replies)
Hi,
I have received an application that stores some properties in a file. The existing struct looks like this:
struct TData
{
UINT uSizeIncludingStrings;
// copy of Telnet data struct
UINT uSize;
// basic properties:
TCHAR szHost; //defined in Sshconfig
UINT iPortNr;
TCHAR... (2 Replies)
Hi,
I am trying to fetch sysname and nodename using struct utsname. I have two HP-UX servers on with 10 characters and other with 13 characters host name. For the first one I am getting truncated 8 characters as output but for the second one i am getting "Value too large to be stored in data type"... (1 Reply)
Hello,
I have a log file for the year, which contains lines starting with the data in the format of YYYY-MM-DD. I need to get all the lines that contain the DD being 04, how would I do this? I tried using grep "*-*04" but it didn't work.
Any quick one liners I should know about?
Thank you. (2 Replies)
Can someone tell me how to do this?
Just a thought that entered my mind when learning about structs.
First thought was:
struct one
{
struct two;
}
struct two
{
three;
}
one->two->three
would this be how you would access "three"? (1 Reply)
I am trying to write binary data to a file. My program below:
#include <stdlib.h>
#include <stdio.h>
struct tinner {
int j;
int k;
};
struct touter {
int i;
struct tinner *inner;
};
int main() {
struct touter data;
data.i = 10;
struct tinner... (4 Replies)
I have 3 columns in an excel sheet.
c1 c2 c3
EIP_ACCOUNT SMALL_TS_01 select A.* from acc;
All the above 3 col shoud be passed a variable in the unix code.
1.How to read an excel file
2.How to pass these data as variable to the unic script (1 Reply)
Hi,
I have a data file formatted like this:
Ex:
Mike 3434
Jack 481
Peter 12
Alan 926
I want to get this data into 2 variables: "Names" and "Numbers" that I can using one "for" loop to get the value as Names and Numbers
Like this:
for i in 0 1 2 3
do
echo $Names
echo... (12 Replies)
04-08-2015
