What do two plus signs in a git diff mean?

Question

I am doing a git diff and for the first time, I am seeing double plus-signs next to lines.

++        if ($field_name == $selected) {
++
++        echo "field_type: {$field['type']}\n";
++        echo "field_name: {$field_name}\n";
++
++        foreach ( $node->$field_name as $language => $value ) {

What does it mean? I googled it, and this result doesn't really explain it. I looked at man and the one example I found doesn't seem to explain it either:

3. It is followed by two-line from-file/to-file header

               --- a/file
               +++ b/file

           Similar to two-line header for traditional unified diff format, /dev/null is used to signal created or deleted files.

What does it mean? I've made changes to the file that are greater than 50% of the previous version. Does it have to do with a file re-write? That's what happened when I committed it.

Answer 1

These lines are added since the last version.

From the manual page:

- static void describe(char *arg)
 -static void describe(struct commit *cmit, int last_one)
++static void describe(char *arg, int last_one)

In the above example output, the function signature was changed from both files (hence two - removals from both file1 and file2, plus ++ to mean one line that was added does not appear in either file1 nor file2). Also eight other lines are the same from file1 but do not appear in file2 (hence prefixed with {plus}).

See diff manual:

https://www.kernel.org/pub/software/scm/git/docs/v1.7.3/git-diff.html