From b697ec448d2ea839eb93c73efeae18b6064d5e32 Mon Sep 17 00:00:00 2001
From: Stefan Frederik <stefan.schippers@gmail.com>
Date: Sun, 13 Feb 2022 12:12:37 +0100
Subject: [PATCH] fix find_nth if multiple / leading separators are present

---
 src/scheduler.c |  9 ++++++++-
 src/token.c     | 19 ++++++++++++-------
 src/xschem.h    |  2 +-
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/src/scheduler.c b/src/scheduler.c
index 15a4a54f..ee1279ab 100644
--- a/src/scheduler.c
+++ b/src/scheduler.c
@@ -741,7 +741,14 @@ int xschem(ClientData clientdata, Tcl_Interp *interp, int argc, const char * arg
   }
 
   else if(argv[1][0] == 'f') {   
-    if(!strcmp(argv[1],"flip"))
+    if(!strcmp(argv[1],"find_nth"))
+    {
+      cmd_found = 1;
+      if(argc > 4) {
+        Tcl_SetResult(interp, find_nth(argv[2], argv[3], atoi(argv[4])), TCL_VOLATILE);
+      }
+    }
+    else if(!strcmp(argv[1],"flip"))
     {
       cmd_found = 1;
       if(! (xctx->ui_state & (STARTMOVE | STARTCOPY) ) ) { 
diff --git a/src/token.c b/src/token.c
index 1ff0e3a1..a19b051e 100644
--- a/src/token.c
+++ b/src/token.c
@@ -2698,11 +2698,10 @@ int isonlydigit(const char *s)
 /* find nth occurrence of substring in str separated by sep. 1st substring is position 1
  * find_nth("aaa,bbb,ccc,ddd", ',', 2)  --> "bbb"
  */
-const char *find_nth(const char *str, char *sep, int n)
+char *find_nth(const char *str, const char *sep, int n)
 {
   static char *result=NULL; /* safe to keep even with multiple schematic windows */
   static int result_size = 0; /* safe to keep even with multiple schematic windows */
-  static const char *empty="";
   int i, len;
   char *ptr;
   int count;
@@ -2710,7 +2709,7 @@ const char *find_nth(const char *str, char *sep, int n)
   if(!str) {
     my_free(1062, &result);
     result_size = 0;
-    return empty;
+    return NULL;
   }
   len = strlen(str) + 1;
   if(len > result_size) {
@@ -2718,19 +2717,25 @@ const char *find_nth(const char *str, char *sep, int n)
     my_realloc(138, &result, result_size);
   }
   memcpy(result, str, len);
-  for(i=0, count=1, ptr=result; result[i] != 0; i++) {
+  i = 0;
+  while(result[i] && strchr(sep, result[i])) i++; /* strip off leading separators */
+  ptr = result + i;
+  for(count=1; result[i] != 0; i++) {
     if(strchr(sep, result[i])) {
       result[i]=0;
       if(count==n) {
         return ptr;
       }
-      while(strchr(sep, result[++i])) ;
-      ptr=result+i;
+      while(result[++i] && strchr(sep, result[i])) ;
+      ptr = result + i;
       count++;
     }
   }
   if(count==n) return ptr;
-  else return empty;
+  else {
+    result[0] = '\0';
+    return result;
+  }
 }
 
 /* substitute given tokens in a string with their corresponding values */
diff --git a/src/xschem.h b/src/xschem.h
index 20eab625..f1f50c07 100644
--- a/src/xschem.h
+++ b/src/xschem.h
@@ -1292,7 +1292,7 @@ extern void int_hash_free(Int_hashentry **table);
 extern Int_hashentry *int_hash_lookup(Int_hashentry **table,
        const char *token, const int value, int what);
 
-extern const char *find_nth(const char *str, char *sep, int n);
+extern char *find_nth(const char *str, const char *sep, int n);
 extern int isonlydigit(const char *s);
 extern const char *translate(int inst, const char* s);
 extern const char* translate2(Lcc *lcc, int level, char* s);