Add a function strings_to_ctypes_array to convert a sequence of strin…

…gs into a ctypes array

pygmt/clib/conversion.py

@@ -2,7 +2,9 @@
 Functions to convert data types into ctypes friendly formats.
 """
 
+import ctypes as ctp
 import warnings
+from collections.abc import Sequence
 
 import numpy as np
 from pygmt.exceptions import GMTInvalidInput
@@ -280,6 +282,32 @@ def kwargs_to_ctypes_array(argument, kwargs, dtype):
     return None
 
 
+def strings_to_ctypes_array(strings: Sequence[str]):
+    """
+    Convert a sequence (e.g., a list) of strings into a ctypes array.
+
+    Parameters
+    ----------
+    strings
+        A sequence of strings.
+
+    Returns
+    -------
+    ctypes_array
+        A ctypes array of strings.
+
+    Examples
+    --------
+    >>> strings = ["first", "second", "third"]
+    >>> ctypes_array = strings_to_ctypes_array(strings)
+    >>> type(ctypes_array)
+    <class 'pygmt.clib.conversion.c_char_p_Array_3'>
+    >>> [s.decode() for s in ctypes_array]
+    ['first', 'second', 'third']
+    """
+    return (ctp.c_char_p * len(strings))(*[s.encode() for s in strings])
+
+
 def array_to_datetime(array):
     """
     Convert a 1-D datetime array from various types into numpy.datetime64.

pygmt/clib/session.py

@@ -20,6 +20,7 @@
     as_c_contiguous,
     dataarray_to_matrix,
     kwargs_to_ctypes_array,
+    strings_to_ctypes_array,
     vectors_to_arrays,
 )
 from pygmt.clib.loading import load_libgmt
@@ -890,13 +891,9 @@ def put_vector(self, dataset, column, vector):
 
         gmt_type = self._check_dtype_and_dim(vector, ndim=1)
         if gmt_type in (self["GMT_TEXT"], self["GMT_DATETIME"]):
-            vector_pointer = (ctp.c_char_p * len(vector))()
             if gmt_type == self["GMT_DATETIME"]:
-                vector_pointer[:] = np.char.encode(
-                    np.datetime_as_string(array_to_datetime(vector))
-                )
-            else:
-                vector_pointer[:] = np.char.encode(vector)
+                vector = np.datetime_as_string(array_to_datetime(vector))
+            vector_pointer = strings_to_ctypes_array(vector)
         else:
             vector_pointer = vector.ctypes.data_as(ctp.c_void_p)
         status = c_put_vector(
@@ -953,13 +950,12 @@ def put_strings(self, dataset, family, strings):
             restype=ctp.c_int,
         )
 
-        strings_pointer = (ctp.c_char_p * len(strings))()
-        strings_pointer[:] = np.char.encode(strings)
-
         family_int = self._parse_constant(
             family, valid=FAMILIES, valid_modifiers=METHODS
         )
 
+        strings_pointer = strings_to_ctypes_array(strings)
+
         status = c_put_strings(
             self.session_pointer, family_int, dataset, strings_pointer
         )