Implement resize function

rosidl_runtime_c/include/rosidl_runtime_c/string_functions.h

@@ -117,6 +117,19 @@ bool
 rosidl_runtime_c__String__assign(
   rosidl_runtime_c__String * str, const char * value);
 
+/// Resize the char pointer.
+/**
+ * This function resize the input value pointer.
+ *
+ * \param[in] n the new size of the internal buffer
+ * \return true if successful, false if the passed string pointer is null
+ *   or if the size is higher than SIZE_MAX or if the memory reallocation failed.
+ */
+ROSIDL_GENERATOR_C_PUBLIC
+bool
+rosidl_runtime_c__String__resize(
+  rosidl_runtime_c__String * str, size_t n);
+
 /// Initialize a rosidl_runtime_c__String__Sequence__init structure.
 /**
  * The rosidl_runtime_c__String__Sequence is initialized with the size passed to the function.

rosidl_runtime_c/src/string_functions.c

@@ -143,6 +143,28 @@ rosidl_runtime_c__String__copy(
     output, input->data, input->size);
 }
 
+bool rosidl_runtime_c__String__resize(
+  rosidl_runtime_c__String *str, size_t n)
+{
+  if(!str) {
+    return false;
+  }
+  // check valid range of n before allocating n + 1 characters
+  if(n > SIZE_MAX / sizeof(char) - 1) {
+    return false;
+  }
+  rcutils_allocator_t allocator = rcutils_get_default_allocator();
+  char * data = allocator.reallocate(str->data, (n + 1) * sizeof(char), allocator.state);
+  if(!data) {
+    return false;
+  }
+  data[n] = 0;
+  str->data = data;
+  str->size = n;
+  str->capacity = n + 1;
+  return true;
+}
+
 bool
 rosidl_runtime_c__String__Sequence__init(
   rosidl_runtime_c__String__Sequence * sequence, size_t size)