LinuxQuestions.org - [SOLVED] To truncate a text file using system call

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To truncate a text file using system call

Hello people,
I am studying a small piece of code to truncate a text file using system call. This is the code.

Code:

#include<stdio.h>

#include<unistd.h>



int main()

{

        int ret;

        ret = truncate("./pirate.txt", 45);

        if(ret==-1)

        {

                perror("truncate");

                return -1;

        }

        return 0;

}

where "pirate.txt" is the existing text file. I execute it through gcc using

Code:

$ gcc trun.c -o trun

$ ./trun

The error is

Code:

bash: ./truncate: No such file or directory

Kindly help. Thank you.

Regards...

pirate.txt is in the same directory as trun ?

@Cedrik
I have edited a pirate.txt file as an example. I do not know its location. How to find out whether they are the same directory?

Hu ? just type "ls" and enter to list files in the current directory

@Cedrik
I moved pirate.txt. Pirate.txt is not in the same directory as trun.

But it has to be in the same dir as trun
"./pirate.txt" => relative path that means file pirate.txt is in the current directory

@Cedrik
I moved pirate.txt again, Now when i run ls command, pirate.txt as well as trun.c are listed in the current directory.
I recompiled and still not able to. Any other alternative? Thanks

Sorry :o

I did not read the error carefully

Code:

bash: ./truncate: No such file or directory

You tried to execute truncate but you named your program "trun"

Try:

Code:

./trun

@Cedrik
Oh no I am sorry too. I wrote two identical programs just to clarify. Truncate.c and Trun.c and misplaced the error code.
I have Executed ./trun too. I am getting the exact same error. :o

I'm confused. Did the compilation succeed and generated a file named "trun" in your current directory?

@ydoom
Compilation is successful, i.e I am getting no errors or warnings after I run $ gcc trun.c -o -trun. After i run ./trun bash says No such file or directory!!?? :Pengy:

Just a side note, I hope: if you run

Code:

gcc trun.c -o -trun

this generates file "-trun" (minus sign in front).

But let's assume that the file "trun" exists :) Try running "strace trun", this return (for me), when there's no file "pirate.txt":

Code:

execve("./trun", ["trun"], [/* 60 vars */]) = 0

brk(0)                                  = 0x804a000

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb77d4000

access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY)      = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=181371, ...}) = 0

mmap2(NULL, 181371, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb77a7000

close(3)                                = 0

open("/lib/libc.so.6", O_RDONLY)        = 3

read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\20o\1\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=1651695, ...}) = 0

mmap2(NULL, 1452456, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7644000

mprotect(0xb77a0000, 4096, PROT_NONE)  = 0

mmap2(0xb77a1000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x15c) = 0xb77a1000

mmap2(0xb77a4000, 10664, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb77a4000

close(3)                                = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7643000

set_thread_area({entry_number:-1 -> 6, base_addr:0xb76436c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0

mprotect(0xb77a1000, 8192, PROT_READ)  = 0

mprotect(0xb77f2000, 4096, PROT_READ)  = 0

munmap(0xb77a7000, 181371)              = 0

truncate("./pirate.txt", 45)            = -1 ENOENT (No such file or directory)

dup(2)                                  = 3

fcntl64(3, F_GETFL)                    = 0x8001 (flags O_WRONLY|O_LARGEFILE)

close(3)                                = 0

write(2, "truncate: No such file or direct"..., 36truncate: No such file or directory) = 36

exit_group(-1)                          = ?

The 6th line from bottom is the failure point. After executing "touch pirate.txt" (creating that file), the output finishes with

Code:

truncate("./pirate.txt", 45)            = 0

exit_group(0)                          = ?

@ydoom
That was the mistake I was making!! I was executing -trun all the time. i just ran $gcc trun.c -o trun, which perfectly worked!!. I appreciate your help. Thanks for your time.