add read_file_to_string to C API

source/api_c/include/c_api.h

@@ -1007,6 +1007,13 @@ extern void DP_ConvertPbtxtToPb(const char* c_pbtxt, const char* c_pb);
  */
 extern void DP_PrintSummary(const char* c_pre);
 
+/**
+ * @brief Read a file to a char array.
+ * @param[in] c_model The name of the file.
+ * @return const char* The char array.
+ */
+const char* DP_ReadFileToChar(const char* c_model);
+
 #ifdef __cplusplus
 } /* end extern "C" */
 #endif

source/api_c/include/deepmd.hpp

@@ -1575,5 +1575,16 @@ class DipoleChargeModifier {
   DP_DipoleChargeModifier *dcm;
   int nsel_types;
 };
+
+/**
+ * @brief Read model file to a string.
+ * @param[in] model Path to the model.
+ * @param[out] file_content Content of the model file.
+ **/
+void inline read_file_to_string(std::string model, std::string &file_content) {
+  const char *c_file_content = DP_ReadFileToChar(model.c_str());
+  file_content = std::string(c_file_content);
+};
+
 }  // namespace hpp
 }  // namespace deepmd

source/api_c/src/c_api.cc

@@ -1134,4 +1134,11 @@ void DP_PrintSummary(const char* c_pre) {
   deepmd::print_summary(pre);
 }
 
+const char* DP_ReadFileToChar(const char* c_model) {
+  std::string model(c_model);
+  std::string file_content;
+  deepmd::read_file_to_string(model, file_content);
+  return string_to_char(file_content);
+}
+
 }  // extern "C"

source/api_c/tests/test_read_file_to_string.cc

@@ -0,0 +1,25 @@
+#include <fcntl.h>
+#include <gtest/gtest.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <algorithm>
+#include <cmath>
+#include <fstream>
+#include <sstream>
+#include <string>
+#include <vector>
+
+#include "deepmd.hpp"
+TEST(TestReadFileToString, readfiletostring) {
+  std::string file_content;
+  deepmd::hpp::read_file_to_string("../../tests/infer/deeppot.txt",
+                                   file_content);
+
+  std::string file_name_2 = "../../tests/infer/deeppot.txt";
+  std::stringstream buffer;
+  std::ifstream file_txt(file_name_2);
+  buffer << file_txt.rdbuf();
+  std::string expected_out_string = buffer.str();
+  EXPECT_STREQ(expected_out_string.c_str(), file_content.c_str());
+}