Add support for empty replaced string

README.md

@@ -5078,12 +5078,14 @@ Replace in the string 'v' from the offset 'start'
 the string 'str1' by the string 'str2' once.
 Returns the offset of the replacement or STRING_FAILURE if no replacement
 was performed.
+str1 shall be a non empty string.
 
 ##### size\_t string\_replace\_all\_str (string\_t v, const char str1[], const char str2[])
 ##### size\_t string\_replace\_all (string\_t v, const string\_t str1, const string\_t str2)
 
 Replace in the string 'v' all the occurences of 
 the string 'str1' by the string 'str2'.
+str1 shall be a non empty string.
 
 ##### void string\_replace\_at (string\_t v, size\_t pos, size\_t len, const char str2[])
 

m-string.h

@@ -887,7 +887,6 @@ string_replace_all_str (string_t v, const char str1[], const char str2[])
   size_t str1_l = strlen(str1);
   size_t str2_l = strlen(str2);
   assert(str1_l > 0);
-  assert(str2_l > 0);
   if (str1_l >= str2_l) {
     stringi_replace_all_str_1ge2(v, str1, str1_l, str2, str2_l );
   } else {

tests/test-mstring.c

@@ -217,6 +217,10 @@ static void test0(void)
   assert (i != STRING_FAILURE);
   assert (string_cmp_str (s1, "Hello, Juliette!") == 0);
 
+  i = string_replace_str (s1, "Juliette", "");
+  assert (i != STRING_FAILURE);
+  assert (string_cmp_str (s1, "Hello, !") == 0);
+
   string_set_str(s1, "Hello world 4 life world is real another world");
   string_replace_all_str(s1, "world", "earth");
   assert( string_equal_str_p(s1, "Hello earth 4 life earth is real another earth"));
@@ -229,6 +233,10 @@ static void test0(void)
   string_replace_all_str(s1, "world", "Wrld");
   assert( string_equal_str_p(s1, "Wrld Hello Wrld 4 life Wrld is real another planet"));
 
+  string_set_str(s1, "Hello world 4 life world is real another world");
+  string_replace_all_str(s1, "world", "");
+  assert( string_equal_str_p(s1, "Hello  4 life  is real another "));
+
   string_set_str(s1, "Hello world 4 life world is real another world");
   string_replace_all_str(s1, "world", "**WORLD**");
   assert( string_equal_str_p(s1, "Hello **WORLD** 4 life **WORLD** is real another **WORLD**"));