use skip_prefix to avoid magic numbers

It's a common idiom to match a prefix and then skip past it
with a magic number, like:

  if (starts_with(foo, "bar"))
	  foo += 3;

This is easy to get wrong, since you have to count the
prefix string yourself, and there's no compiler check if the
string changes.  We can use skip_prefix to avoid the magic
numbers here.

Note that some of these conversions could be much shorter.
For example:

  if (starts_with(arg, "--foo=")) {
	  bar = arg + 6;
	  continue;
  }

could become:

  if (skip_prefix(arg, "--foo=", &bar))
	  continue;

However, I have left it as:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = v;
	  continue;
  }

to visually match nearby cases which need to actually
process the string. Like:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = atoi(v);
	  continue;
  }

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 10 deletions

diff --git a/git.c b/git.c
index 7780572..b2bb09e 100644
--- a/git.c
+++ b/git.c
@@ -54,8 +54,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 		/*
 		 * Check remaining flags.
 		 */
-		if (starts_with(cmd, "--exec-path")) {
-			cmd += 11;
+		if (skip_prefix(cmd, "--exec-path", &cmd)) {
 			if (*cmd == '=')
 				git_set_argv_exec_path(cmd + 1);
 			else {
@@ -92,8 +91,8 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				*envchanged = 1;
 			(*argv)++;
 			(*argc)--;
-		} else if (starts_with(cmd, "--git-dir=")) {
-			setenv(GIT_DIR_ENVIRONMENT, cmd + 10, 1);
+		} else if (skip_prefix(cmd, "--git-dir=", &cmd)) {
+			setenv(GIT_DIR_ENVIRONMENT, cmd, 1);
 			if (envchanged)
 				*envchanged = 1;
 		} else if (!strcmp(cmd, "--namespace")) {
@@ -106,8 +105,8 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				*envchanged = 1;
 			(*argv)++;
 			(*argc)--;
-		} else if (starts_with(cmd, "--namespace=")) {
-			setenv(GIT_NAMESPACE_ENVIRONMENT, cmd + 12, 1);
+		} else if (skip_prefix(cmd, "--namespace=", &cmd)) {
+			setenv(GIT_NAMESPACE_ENVIRONMENT, cmd, 1);
 			if (envchanged)
 				*envchanged = 1;
 		} else if (!strcmp(cmd, "--work-tree")) {
@@ -120,8 +119,8 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				*envchanged = 1;
 			(*argv)++;
 			(*argc)--;
-		} else if (starts_with(cmd, "--work-tree=")) {
-			setenv(GIT_WORK_TREE_ENVIRONMENT, cmd + 12, 1);
+		} else if (skip_prefix(cmd, "--work-tree=", &cmd)) {
+			setenv(GIT_WORK_TREE_ENVIRONMENT, cmd, 1);
 			if (envchanged)
 				*envchanged = 1;
 		} else if (!strcmp(cmd, "--bare")) {
@@ -578,8 +577,7 @@ int main(int argc, char **av)
 	 * So we just directly call the builtin handler, and die if
 	 * that one cannot handle it.
 	 */
-	if (starts_with(cmd, "git-")) {
-		cmd += 4;
+	if (skip_prefix(cmd, "git-", &cmd)) {
 		argv[0] = cmd;
 		handle_builtin(argc, argv);
 		die("cannot handle %s as a builtin", cmd);