Question

I know, that if i want to compare two structs than i have to write it for myself, because there isn’t any function for this, but i can’t figure out how should i do that. I have three structs : primary, secondarystruct, and difference(this should contain the different items). All three has the following members : char * filename, char * size, int size.

All i need are those items which aren’t in the secondarystruct , or if they are then i need them only if their size is bigger then the secondarystruct’s size. Hope you understand what i want. My english isn’t the best, sorry for this.

Here is what i tried:

j = 0;
x = 0;
for ( i = 0; i < primarypcs; )
{
    memset( tmp, 0, sizeof( tmp ) );
    l = 1;
    for ( k = 0; k < strlen( primary[i].filename );k++ )
    {
        tmp[k] = primary[i].filename[l];
        l++;
    }
    tmp[k]='\0';

    memset( buf, 0, sizeof( buf ) );
    l = 1;
    for ( k = 0; k < strlen( secondarystruct[j].filename ); k++ ) //<-- here is where my program freezes
    {
        buf[k] = secondarystruct[j].filename[l];
        l++;
    }
    buf[k]='\0';

    if ( ( stricmp( tmp, buf ) == 0 ) && ( x == 0 ) )
    {
        if ( primary[i].intsize > secondarystruct[j].intsize )
        {
            difference[diff].filename = strdup( primary[i].filename );
            difference[diff].size = strdup( primary[i].size );
            difference[diff].intsize = -1;
            diff++;
            i++;
            if ( j == secondarypcs ) x = 1;
            else j++;
        }
        else if ( x == 0 )
        {
            i++;
            if ( j == secondarypcs ) x = 1;
            else j++;
        }
    }
    else
    {
        difference[diff].filename = strdup( primary[i].filename );
        difference[diff].size = strdup( primary[i].size );
        difference[diff].intsize = -1;
        diff++;
        i++;
    }
}

Please tell me what i’m doing wrong!

Thanks, kampi

Update:

Sorry, it seems, i gave you not enough information.
So: both structures are containing file list, from different drives, like “C:\” and “D:\”. This is the reason why i can’t use just simple strcmp, because the first letter will always differ. That’s why i have to “cut them off” and then compare. This program should work like this: It retrieves the file list from c:\ and then retrieves the filelist from d:\ and then compares them. If on file which is on c:\ doesn’t exists on d:\ then it should be copied there, if on d:\ there is a file which doesn’t exists on c:\ then it should be ignored(i don’t wan’t to do with it anything). If a file which is found in c:\ and d:\ as well, then i wan’t to copy it only then if the file from c:\ has a bigger size than a file which is on d:\

Hope you understand now what i want.

Answer 1

The most probable cause of your “freeze” is the strlen() call, which is likely caused by some memory problem (ie. that its argument isn’t a pointer to string terminated by zero). There may be multiple causes of this:

• you may have overwritten some of your memory by a buffer overflow (of tmp or buf).
• I assume you’re using x as an indicator you’ve gone to the end, but you use secondarystruct[j] after that. Moreover, if secondarypcs has the same meaning as primarypcs, that is, the count of elements of an array, you’re using secondarystruct[secondarypcs], but that’s out-of-bounds.

Some other tips:

• if the first file in secondarypcs is missing in primarypcs, your code will put everything to diff, no matter what.

• comparing the strings regardless of the first letter can be done like this:

  (*str1 && *str2 ? strcmp(str1+1, str2+1) : -1)

I’d suggest code like this:

void add_to_difference(struct diff_file* f);

...

// assuming primarystruct and secondarystruct are arrays of diff_file sorted by filename
j=0;
for(i=0; i<primarypcs; i++) {
  // find a passibly matching secondary file
  while(j<secondarypcs && strcmp(primarystruct[i].filename+1, secondarystruct[j].filename+1)<0)
    j++;
  // not found... add all overflow items to diff
  if(j>=secondarypcs) {
    for(; i<primarypcs; i++)
      add_to_diff(primarystruct+i);
    break;
  }
  // do the comparison
  if(strcmp(primarystruct[i].filename+1, secondarystruct[j].filename+1)>0 || 
    primarystruct[i].intsize>secondarystruct[j].intsize)
    add_to_diff(primarystruct+i);
  // that's it
}