First of all thanks for the help you giving to me.
I am new in programming. Actually i am studying in informatics. That's also the reason my code is a mess, i mean lining and everything ...
I tried to fix it...
Code:
//multiply a[2][3] * b[3][4] = c[2][4]
//with fork
//each child completes one c[2][4]'s row
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
main()
{
int a[2][3] = {1,2,3,
4,5,6};
int b[3][4] = {1,2,3,4,
5,6,7,8,
9,10,11,12};
int c[2][4] = { 0 };
int i, j;
int n; //common 3
int pid;
int pipefd[2];
int w, data_len;
char buff[100];
char str[100+1] = {'\0'};
for ( i=0;i<2;i++ )
{
pipe(pipefd);
if( pipefd < 0 )
printf("Pipe error\n");
pid = fork();
if( pid == -1 )
{
printf("Can't fork\n");
}
if( pid == 0 )//child
{
for( j=0;j<4;j++ )
{
for( n=0;n<3;n++ )
{
c[i][j] += a[i][n]*b[n][j];
}
sprintf( str, "%d ", c[i][j] );
w = write( pipefd[1], str, sizeof (str) );
if( w != sizeof (str) )
printf("\nWrite error");
}
exit(0);
}
if( pid > 0 )//parent
{
wait(0);
if( ( data_len = read( pipefd[0], buff, sizeof ( buff ) ) ) <=0 )
{
fprintf( stderr,"Read failed: %d\n", strerror( errno ) ); //%s gives me a warning so i checked man errno and
exit(1); //change it to %d
}
sscanf( buff, "%d %d %d %d", &c[i][0], &c[i][1], &c[i][2], &c[i][3]);
}
}
printf("C:\n");
for( i=0;i<2;i++ )
{
for( j=0;j<4;j++ )
{
printf("%d\t",c[i][j]);
}
printf("\n");
}
}
Almost done!
I get no Segmentation fault, no errors or warnings in compiling!
But C array has the right numbers only in c[0][0] and c[1][0], at others i get 0s.
So its like this:
Hi
$ a=10 ; b=2
$ expr $a + $b
12
$ expr $a - $b
8
$ expr $a / $b
5
$ expr $a * $b
expr: syntax error
Any idean why I am getting this error only when multiplying two numbers. Whats the exact syntax?
Thanks a lot to all in advance
CSaha (5 Replies)
Is there a way that i can get something like this to work:
Number=`expr 80 \* 10.69`
i.e. To multiply an integer by a decimal or a decimal by a decimal etc...?
thanks (10 Replies)
Im very new to programming. But I would like to write a script which extracts and multiply values from 2 txt and output as a new file. Can someone please teach me how to write it? Thank you so much
for example
File A File B
1 34 1 2
2 13 2 2
3 8 3 3
File C output
1 68
2... (2 Replies)
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Hi, this is my code.It's simple : there are 2 2D arrays and the multiplied to C.
#include<stdio.h>
#include<sys/shm.h>
#include<sys/stat.h>
#include<stdlib.h>
main()
{
int *A; //A
int *B; //B
int *C; //C
int i,j,x,k,d;
int id;
... (17 Replies)
hello,
I'm writing a php script in fedora to run with a csv file. I want the script to read column 4 and multiply each single line in the column by 1000, how would that script look? I've written one script but it's obviously incorrect because it will not execute the command.
here is my... (4 Replies)
I am trying to take all the elements of an array and multiply them by 2, and then copy them to a new array. Here is what I have
i=0
for true in DMGLIST
do
let DMGSIZES2="${DMGSIZES}"*2
let i++
done
unset i
echo ${DMGSIZES2}
It does the calculation correctly for the first element,... (7 Replies)
I have 2 files, that look like this:
ID SNP1 SNP2 SNP3 SNP4
A1 1 2 0 2
A2 2 0 1 1
A3 0 2 NA 1
A4 1 1 0 2
and this:
SNP score
SNP1 0.5
SNP2 0.7
SNP3 0.8
SNP4 0.2
Basically, all of the SNP-values are 0,1, 2 or NA, and they each have a score, listed in the second file. The total... (5 Replies)
Hi Experts,
Please help with the following.
I have 3 columns in File 1 , variables with values nested within groups.
File 1
gr1 var1 a
gr1 var2 b
gr1 var3 a
gr1 var4 c
gr2 var1 a
gr2 var2 a
gr2 var4 c
gr3 var1 b
gr3 var3 b
gr3 var4 a
gr3 var5 a (3 Replies)
I am trying to remove the last letter in a file and then multiply each line (which contained this letter) by 500. This is what I have:
1499998A
1222222A
1325804A
1254556
1235
9998
777
cat /tmp/listzz |gawk '{print $4}'|gawk '{gsub(//, ""); print } This removes the A... (1 Reply)
Discussion started by: newbie2010
1 Replies
LEARN ABOUT DEBIAN
pipe
PIPE(2) Linux Programmer's Manual PIPE(2)NAME
pipe, pipe2 - create pipe
SYNOPSIS
#include <unistd.h>
int pipe(int pipefd[2]);
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h> /* Obtain O_* constant definitions */
#include <unistd.h>
int pipe2(int pipefd[2], int flags);
DESCRIPTION
pipe() creates a pipe, a unidirectional data channel that can be used for interprocess communication. The array pipefd is used to return
two file descriptors referring to the ends of the pipe. pipefd[0] refers to the read end of the pipe. pipefd[1] refers to the write end
of the pipe. Data written to the write end of the pipe is buffered by the kernel until it is read from the read end of the pipe. For fur-
ther details, see pipe(7).
If flags is 0, then pipe2() is the same as pipe(). The following values can be bitwise ORed in flags to obtain different behavior:
O_NONBLOCK Set the O_NONBLOCK file status flag on the two new open file descriptions. Using this flag saves extra calls to fcntl(2) to
achieve the same result.
O_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the two new file descriptors. See the description of the same flag in open(2) for
reasons why this may be useful.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EFAULT pipefd is not valid.
EINVAL (pipe2()) Invalid value in flags.
EMFILE Too many file descriptors are in use by the process.
ENFILE The system limit on the total number of open files has been reached.
VERSIONS
pipe2() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.
CONFORMING TO
pipe(): POSIX.1-2001.
pipe2() is Linux-specific.
EXAMPLE
The following program creates a pipe, and then fork(2)s to create a child process; the child inherits a duplicate set of file descriptors
that refer to the same pipe. After the fork(2), each process closes the descriptors that it doesn't need for the pipe (see pipe(7)). The
parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a
time from the pipe and echoes it on standard output.
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char *argv[])
{
int pipefd[2];
pid_t cpid;
char buf;
if (argc != 2) {
fprintf(stderr, "Usage: %s <string>
", argv[0]);
exit(EXIT_FAILURE);
}
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
cpid = fork();
if (cpid == -1) {
perror("fork");
exit(EXIT_FAILURE);
}
if (cpid == 0) { /* Child reads from pipe */
close(pipefd[1]); /* Close unused write end */
while (read(pipefd[0], &buf, 1) > 0)
write(STDOUT_FILENO, &buf, 1);
write(STDOUT_FILENO, "
", 1);
close(pipefd[0]);
_exit(EXIT_SUCCESS);
} else { /* Parent writes argv[1] to pipe */
close(pipefd[0]); /* Close unused read end */
write(pipefd[1], argv[1], strlen(argv[1]));
close(pipefd[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
}
}
SEE ALSO fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-02-14 PIPE(2)