2 files changed, 45 insertions, 10 deletions

diff --git a/include/util/string.h b/include/util/string.h
index 3f1cb0c..6e6496c 100644
--- a/include/util/string.h
+++ b/include/util/string.h
@@ -10,8 +10,10 @@
 namespace ov4
 {
 
-void string2argv(const std::vector<std::string> &s, char **argv);
-void argv2string(std::vector<std::string> &s, const char * const * argv);
+void string2argv(const std::vector<std::string> &v, char **argv);
+char **string2argv(const std::vector<std::string> &v);
+void argv2string(std::vector<std::string> &v, const char * const * argv);
+size_t argv_get_required_size(std::vector<std::string> &v);
 std::string safe_str(const char *s, const char *fallback = "");
 void print_str_hex(const std::string &s);
     
diff --git a/src/util/string.cc b/src/util/string.cc
index 9fad804..3bf34f7 100644
--- a/src/util/string.cc
+++ b/src/util/string.cc
@@ -7,36 +7,69 @@ using namespace std;
 namespace ov4
 {
 
-void string2argv(const vector<string> &s, char **argv)
+/*
+ * construct C-style **argv
+ * user should be responsible for allocation of **argv
+ * and make sure it's large enough
+ * argv should be the address to an empty and continuous memory space
+ */
+void string2argv(const vector<string> &v, char **argv)
 {
 
     // pointers [0, size)
     // nullptr [size]
     // data  [size+1, ...)
 
-    char *p = (char*)(argv + s.size() + 1);
+    char *p = (char*)(argv + v.size() + 1);
 
-    argv[s.size()] = nullptr;
+    argv[v.size()] = nullptr;
 
-    for (size_t i = 0; i < s.size(); i++)
+    for (size_t i = 0; i < v.size(); i++)
     {
-        strcpy(p, s[i].c_str());
+        strcpy(p, v[i].c_str());
         argv[i] = p;
-        p += s[i].size() + 1; // for '\0'
+        p += v[i].size() + 1; // for '\0'
     }
 }
 
-void argv2string(vector<string> &s, const char * const * argv)
+/*
+ * allocate heap memory, and construct C-style **argv
+ * NB: user should be responsible to ::operator delete();
+ */
+char **string2argv(const std::vector<std::string> &v)
+{
+    size_t size = argv_get_required_size(v);
+    char **p = static_cast<char**>(operator new(size));
+    string2argv(v, p);
+    return p;
+}
+
+void argv2string(vector<string> &v, const char * const * argv)
 {
     if (argv == nullptr) return; 
+
+    v.clear();
     
     for (size_t i = 0; true; i++)
     {
         if (argv[i] == nullptr) return;
-        s.push_back(argv[i]);
+        v.push_back(argv[i]);
     }
 }
 
+/*
+ * return the memory size required to construct argv[][]
+ * in byte
+ */
+size_t argv_get_required_size(const std::vector<std::string> &v)
+{
+    size_t ret = 0; 
+    ret += sizeof(char*) * (v.size() + 1); // point to every strings in v, and nullptr terminator
+    for (auto &sub : v)
+        ret += sizeof(char) * (sub.size() + 1); // chars, and null terminator
+    return ret;
+}
+
 std::string safe_str(const char *s, const char *fallback)
 {
     return (s != nullptr) ? s : fallback;