Question

I modified line 494 of a certain file, and use cvs diff -u4 to see what I have modified, cvs outputs something like :

@@ -490,9 +490,9 @@         
if (!(hPtr->hStatus & (HOST_STAT_UNAVAIL | HOST_STAT_UNLICENSED |
                       HOST_STAT_UNREACH))){ 
            printf(" %s:\n",
            _i18n_msg_get(ls_catd,NL_SETN,1612, "CURRENT LOAD USED FOR SCHEDULING")); /* catgets  1612  */
    -       prtLoad(hPtr, lsInfo);
    +       prtLoad(hPtr, lsInfo,bhostParams);

            if (lsbSharedResConfigured_) {
            /* there are share resources */
            retVal = makeShareFields(hPtr->host, lsInfo, &nameTable,

I didn’t understand what the first line “@@ -490,9 +490,9 @@” mean, I did modify line 494, but why CVS writes 490 instead? Could anyone tell me what does “@@ -490,9 +490,9 @@” mean?

Answer 1

The “u” gives you a unified diff and the “4” give you 4 lines of context on either side. From the WP entry I just linked:

The format of the range information line is as follows:

@@ -l,s +l,s @@

The hunk range information contains two hunk ranges. The range for the
hunk of the original file is preceded by a minus symbol, and the range
for the new file is preceded by a plus symbol. Each hunk range is of
the format l,s where l is the starting line number and s is the number
of lines the change hunk applies to for each respective file.

So basically the number isn’t the line that was changed. It’s the start of the range being displayed in that hunk. Using your example, the hunk starts at line 490 and 9 lines were in the range. The reason the range covers 9 lines is because of the one line you changed and the four lines of context on either side.

Note that your example seems to have some newlines stripped. I would recommend you fix it so it is clear for other people.