Add rcutils_string_array_sort function

include/rcutils/types/string_array.h

@@ -113,11 +113,11 @@ rcutils_string_array_fini(rcutils_string_array_t * string_array);
 
 /// Compare two string arrays.
 /**
- * The two string arrays are compared according to lexographical order.
+ * The two string arrays are compared according to lexicographical order.
  *
  * \param[in] sa0 The first string array.
  * \param[in] sa1 The second string array.
- * \param[out] res Negative value if `lhs` appears before `rhs` in lexographical order.
+ * \param[out] res Negative value if `lhs` appears before `rhs` in lexicographical order.
  *   Zero if `lhs` and `rhs` are equal.
  *   Positive value if `lhs` appears after `rhs in lexographical order.
  * \return `RCUTILS_RET_OK` if successful, or
@@ -133,6 +133,22 @@ rcutils_string_array_cmp(
   const rcutils_string_array_t * rhs,
   int * res);
 
+/// Sort a string array according to lexicographical order.
+/**
+ * This function changes the order of the entries in a string array so that
+ * they are in lexicographically ascending order. Empty entries are placed at the
+ * end of the array.
+ *
+ * \param[inout] string_array object whose elements should be sorted.
+ * \return `RCUTILS_RET_OK` if successful, or
+ * \return `RCUTILS_RET_INVALID_ARGUMENT` for invalid arguments, or
+ * \return `RCUTILS_RET_ERROR` if an unknown error occurs
+ */
+RCUTILS_PUBLIC
+RCUTILS_WARN_UNUSED
+rcutils_ret_t
+rcutils_string_array_sort(rcutils_string_array_t * string_array);
+
 #ifdef __cplusplus
 }
 #endif

src/string_array.c

@@ -133,6 +133,37 @@ rcutils_string_array_cmp(
   return RCUTILS_RET_OK;
 }
 
+static int
+rcutils_string_array_sort_compare(const void * lhs, const void * rhs)
+{
+  const char * left = *(const char **)lhs;
+  const char * right = *(const char **)rhs;
+  if (NULL == left) {
+    return NULL == right ? 0 : 1;
+  } else if (NULL == right) {
+    return -1;
+  }
+  return strcmp(left, right);
+}
+
+rcutils_ret_t
+rcutils_string_array_sort(rcutils_string_array_t * string_array)
+{
+  RCUTILS_CHECK_FOR_NULL_WITH_MSG(
+    string_array, "string_array is null", return RCUTILS_RET_INVALID_ARGUMENT);
+
+  if (1 >= string_array->size) {
+    return RCUTILS_RET_OK;
+  }
+
+  RCUTILS_CHECK_FOR_NULL_WITH_MSG(
+    string_array->data, "string_array->data is null", return RCUTILS_RET_INVALID_ARGUMENT);
+
+  qsort(string_array->data, string_array->size, sizeof(char *), rcutils_string_array_sort_compare);
+
+  return RCUTILS_RET_OK;
+}
+
 #ifdef __cplusplus
 }
 #endif

test/test_string_array.cpp

@@ -130,3 +130,60 @@ TEST(test_string_array, string_array_cmp) {
   ret = rcutils_string_array_fini(&incomplete_string_array);
   ASSERT_EQ(RCUTILS_RET_OK, ret);
 }
+
+TEST(test_string_array, string_array_sort) {
+  auto allocator = rcutils_get_default_allocator();
+  rcutils_ret_t ret;
+
+  ret = rcutils_string_array_sort(nullptr);
+  EXPECT_EQ(RCUTILS_RET_INVALID_ARGUMENT, ret);
+
+  rcutils_string_array_t sa0 = rcutils_get_zero_initialized_string_array();
+  ret = rcutils_string_array_sort(&sa0);
+  EXPECT_EQ(RCUTILS_RET_OK, ret);
+
+  ret = rcutils_string_array_init(&sa0, 8, &allocator);
+  ASSERT_EQ(RCUTILS_RET_OK, ret);
+
+  // Already in order
+  for (size_t i = 0; i < sa0.size; i++) {
+    const char val[] = {static_cast<char>('a' + i), '\0'};
+    sa0.data[i] = strdup(val);
+  }
+
+  ret = rcutils_string_array_sort(&sa0);
+  EXPECT_EQ(RCUTILS_RET_OK, ret);
+  for (size_t i = 0; i < sa0.size; i++) {
+    const char val[] = {static_cast<char>('a' + i), '\0'};
+    EXPECT_STREQ(val, sa0.data[i]);
+  }
+
+  // Reverse order
+  for (size_t i = 0; i < sa0.size; i++) {
+    const char val[] = {static_cast<char>('a' + sa0.size - 1 - i), '\0'};
+    sa0.data[i] = strdup(val);
+  }
+
+  ret = rcutils_string_array_sort(&sa0);
+  EXPECT_EQ(RCUTILS_RET_OK, ret);
+  for (size_t i = 0; i < sa0.size; i++) {
+    const char val[] = {static_cast<char>('a' + i), '\0'};
+    EXPECT_STREQ(val, sa0.data[i]);
+  }
+
+  // Make some entries empty
+  for (size_t i = 0; i < sa0.size / 2; i++) {
+    sa0.allocator.deallocate(sa0.data[i], sa0.allocator.state);
+    sa0.data[i] = nullptr;
+  }
+
+  ret = rcutils_string_array_sort(&sa0);
+  EXPECT_EQ(RCUTILS_RET_OK, ret);
+  for (size_t i = 0; i < sa0.size / 2; i++) {
+    const char val[] = {static_cast<char>('a' + i + (sa0.size / 2)), '\0'};
+    EXPECT_STREQ(val, sa0.data[i]);
+  }
+  for (size_t i = sa0.size / 2; i < sa0.size; i++) {
+    EXPECT_STREQ(nullptr, sa0.data[i]);
+  }
+}