passing integers in place of file descriptor when calling write command in c

void main()

{



     pid_t  pid;

     int    i;

     char   buf[BUF_SIZE];

     fork();

     pid = getpid();

     for (i = 1; i <= MAX_COUNT; i++) {

          sprintf(buf, "This line is from pid %d, value = %dn", pid, i);

          write(1, buf, strlen(buf));

        // printf("%s",buf);

     }

}

I've got the given simple code to show fork process in c. I noticed that when I pass any value greater than 2 in place of 1 in write command the code does not print anything. Why is this happening?

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

asked Nov 21 '18 at 21:19

Ashray Sinha

2

You should check the return value of write for an error.

– Fiddling Bits
Nov 21 '18 at 21:20

1 is for standard output descriptor, 2 is for error. Others aren't open

– Jean-François Fabre
Nov 21 '18 at 21:24

note that the fork part is irrelevant to the question. The example could be reduced even more to only include a write call.

– Jean-François Fabre
Nov 21 '18 at 21:31

add a comment |

void main()

{



     pid_t  pid;

     int    i;

     char   buf[BUF_SIZE];

     fork();

     pid = getpid();

     for (i = 1; i <= MAX_COUNT; i++) {

          sprintf(buf, "This line is from pid %d, value = %dn", pid, i);

          write(1, buf, strlen(buf));

        // printf("%s",buf);

     }

}

I've got the given simple code to show fork process in c. I noticed that when I pass any value greater than 2 in place of 1 in write command the code does not print anything. Why is this happening?

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

asked Nov 21 '18 at 21:19

Ashray Sinha

2

You should check the return value of write for an error.

– Fiddling Bits
Nov 21 '18 at 21:20

1 is for standard output descriptor, 2 is for error. Others aren't open

– Jean-François Fabre
Nov 21 '18 at 21:24

note that the fork part is irrelevant to the question. The example could be reduced even more to only include a write call.

– Jean-François Fabre
Nov 21 '18 at 21:31

add a comment |

void main()

{



     pid_t  pid;

     int    i;

     char   buf[BUF_SIZE];

     fork();

     pid = getpid();

     for (i = 1; i <= MAX_COUNT; i++) {

          sprintf(buf, "This line is from pid %d, value = %dn", pid, i);

          write(1, buf, strlen(buf));

        // printf("%s",buf);

     }

}

I've got the given simple code to show fork process in c. I noticed that when I pass any value greater than 2 in place of 1 in write command the code does not print anything. Why is this happening?

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

asked Nov 21 '18 at 21:19

Ashray Sinha

void main()

{



     pid_t  pid;

     int    i;

     char   buf[BUF_SIZE];

     fork();

     pid = getpid();

     for (i = 1; i <= MAX_COUNT; i++) {

          sprintf(buf, "This line is from pid %d, value = %dn", pid, i);

          write(1, buf, strlen(buf));

        // printf("%s",buf);

     }

}

I've got the given simple code to show fork process in c. I noticed that when I pass any value greater than 2 in place of 1 in write command the code does not print anything. Why is this happening?

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

asked Nov 21 '18 at 21:19

Ashray Sinha

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

asked Nov 21 '18 at 21:19

Ashray Sinha

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

edited Nov 21 '18 at 21:22

NathanOliver

92.7k16129195

asked Nov 21 '18 at 21:19

Ashray Sinha

asked Nov 21 '18 at 21:19

Ashray Sinha

asked Nov 21 '18 at 21:19

Ashray Sinha

2

You should check the return value of write for an error.

– Fiddling Bits
Nov 21 '18 at 21:20

1 is for standard output descriptor, 2 is for error. Others aren't open

– Jean-François Fabre
Nov 21 '18 at 21:24

note that the fork part is irrelevant to the question. The example could be reduced even more to only include a write call.

– Jean-François Fabre
Nov 21 '18 at 21:31

add a comment |

2

You should check the return value of write for an error.

– Fiddling Bits
Nov 21 '18 at 21:20

1 is for standard output descriptor, 2 is for error. Others aren't open

– Jean-François Fabre
Nov 21 '18 at 21:24

note that the fork part is irrelevant to the question. The example could be reduced even more to only include a write call.

– Jean-François Fabre
Nov 21 '18 at 21:31

You should check the return value of write for an error.

– Fiddling Bits
Nov 21 '18 at 21:20

1 is for standard output descriptor, 2 is for error. Others aren't open

– Jean-François Fabre
Nov 21 '18 at 21:24

note that the fork part is irrelevant to the question. The example could be reduced even more to only include a write call.

– Jean-François Fabre
Nov 21 '18 at 21:31

add a comment |

1 Answer
1

active

oldest

votes

you're performing a raw write call where at the start of your program:

1 is the standard output descriptor

2 is the standard error descriptor

Both write to the console by default (and 0 is the standard input, cannot be written to)

Other descriptors are invalid unless they've been returned by an open call. Since you don't check the return value of write, you can't see that an error code is returned (probably EBADF, bad file descriptor)

edited Nov 21 '18 at 21:30

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

add a comment |

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1 Answer
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active

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1 Answer
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active

oldest

votes

you're performing a raw write call where at the start of your program:

1 is the standard output descriptor

2 is the standard error descriptor

Both write to the console by default (and 0 is the standard input, cannot be written to)

edited Nov 21 '18 at 21:30

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

add a comment |

you're performing a raw write call where at the start of your program:

1 is the standard output descriptor

2 is the standard error descriptor

Both write to the console by default (and 0 is the standard input, cannot be written to)

edited Nov 21 '18 at 21:30

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

add a comment |

you're performing a raw write call where at the start of your program:

1 is the standard output descriptor

2 is the standard error descriptor

Both write to the console by default (and 0 is the standard input, cannot be written to)

edited Nov 21 '18 at 21:30

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

you're performing a raw write call where at the start of your program:

1 is the standard output descriptor

2 is the standard error descriptor

Both write to the console by default (and 0 is the standard input, cannot be written to)

edited Nov 21 '18 at 21:30

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

edited Nov 21 '18 at 21:30

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

answered Nov 21 '18 at 21:25

Jean-François Fabre

104k955112

add a comment |

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