CODEWITHSUNDEEP
cfreadprintffile-copying
Ajish Alfred
Ajish Alfred

Reputation: 155

segmentation fault while copying file

I'm a beginner and I'm trying to copy the content of a very large text file of size around 33MB ( 33136KB precisely ) to a new file. I'm getting segmentation fault while running the program. Only 16KB is getting copied to my new file. The name of file which I'm to copy is "test_file3" and my new file's name is "newfile". I'm doing all this in CentOS-5 in virtual box. Here is the details:

[root@localhost decomp_trials]# cat read_file.c

    #include <stdio.h>
    #include <stdlib.h>

    int main( int argc, char *argv [] )
    {
            FILE *ifp, *ofp;
            char *ptr;

            ifp = fopen ( argv [ 1 ], "r" );
            ofp = fopen ( argv [ 2 ], "a" );

            for (  ptr = malloc ( 10 ); fread ( ptr, 1, 10, ifp ); )
                    fprintf ( ofp, ptr );

            fclose ( ifp );
            fclose ( ofp );

            return 0;
    }

[root@localhost decomp_trials]# cc read_file.c -o read_file
[root@localhost decomp_trials]# ./read_file /root/sys_cl_huk_ajh/imp/copy_hook7/test_file3 newfile
Segmentation fault
[root@localhost decomp_trials]# du -s newfile 
16      newfile
[root@localhost decomp_trials]# pwd
/root/sys_cl_huk_ajh/pro_jnk/decomp_trials
[root@localhost decomp_trials]# du -s ../../imp/copy_hook7/test_file3
33136   ../../imp/copy_hook7/test_file3
[root@localhost decomp_trials]#

Please tell me what I'm possibly doing wrong. Is there any better method? Please help me out

Upvotes: 1

Views: 310

Answers (1)

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272507

Don't use fprintf; it treats its second argument as a format string. Use fwrite.

As to why it seg-faults, consider what happens if your input data happens to contain e.g. %s. fprintf will then start walking through the stack, reading random data until it finds a 0-valued byte (a null terminator). This could easily end up walking into memory that isn't owned by the application.

Upvotes: 2

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