用C清理正则表达式代码？

Question

I've got a C program that processes output from some shell commands. For 'ps', I'm interested in the following five fields. I specify the fields that I want by name, build the pattern for the glib regex engine, and then parse and process the results.

Is there a good way to organize fields, patterns, and formats/types that yields readable and maintainable code? What I have so far works, but doesn't look so good. I'm developing on OS X, but will want to port to other platforms later.

Also is there a way to get behavior like C#'s @ string operator to eliminate half my back slashes in the patterns?

Thanks.

const char field_pid[] = "pid";
const char field_lstart[] = "lstart";
const char field_ruser[] = "ruser";
const char field_cputime[] = "cputime";
const char field_command[] = "command";

char pattern[] = "\\s*(?<pid>\\d+)\\s+(?<lstart>\\w+\\s+\\w+\\s+\\d+\\s+[\\d:]+\\s+\\d+)\\s+(?<ruser>\\w+)\\s+(?<cputime>[\\d:\\.]+)\\s+(?<command>.+)";

// Do the regex match.
...

// Extract the matching strings.
gchar *pid = g_match_info_fetch_named(match_info, field_pid);
gchar *lstart = g_match_info_fetch_named(match_info, field_lstart);
gchar *ruser = g_match_info_fetch_named(match_info, field_ruser);
gchar *cputime = g_match_info_fetch_named(match_info, field_cputime);
gchar *command = g_match_info_fetch_named(match_info, field_command);

// Parse and process the strings.
...

Answer 1

Here are several improvement options:

• use the G_REGEX_EXTENDED option to compile the pattern. This will make whitespace in the pattern ignored, and # can be used to introduce comments until end of line.

• split the regex into several lines.

• read the regex from an external file instead of picking it up from the C source. (You can write a utility function for this, or use glib's configuration reading mechanisms.) This is the only way to cure the backslashitis.

Barring the last suggestion, the resulting regex might look like this:

const char *pattern = "\
\\s*                                  \
(?<pid> \\d+ ) \\s+                   \
(?<lstart> \\w+ \\s+ \\w+ \\s+ \\d+ \\s+ [\\d:]+ \\s+ \\d+) \\s+    \
(?<ruser> \\w+) \\s+                  \
(?<cputime> [\\d:\\.]+) \\s+          \
(?<command> .+)                       \
"

Still far from perfect, but much more readable than what you started with.