add custom constructor for TextFileReader that uses an already opened file descriptor

src/text_file_reader.cpp

@@ -41,7 +41,7 @@ using namespace LAMMPS_NS;
  * \param  filetype  Description of file type for error messages */
 
 TextFileReader::TextFileReader(const std::string &filename, const std::string &filetype)
-  : filename(filename), filetype(filetype), ignore_comments(true)
+  : filetype(filetype), ignore_comments(true)
 {
   fp = fopen(filename.c_str(), "r");
 
@@ -51,6 +51,18 @@ TextFileReader::TextFileReader(const std::string &filename, const std::string &f
   }
 }
 
+/**
+ * \overload
+ *
+ * \param  fp        File descriptor of the already opened file
+ * \param  filetype  Description of file type for error messages */
+
+TextFileReader::TextFileReader(FILE *fp, const std::string &filetype)
+  : filetype(filetype), fp(fp), ignore_comments(true)
+{
+  if (fp == nullptr) throw FileReaderException("Invalid file descriptor");
+}
+
 /** Closes the file */
 
 TextFileReader::~TextFileReader() {

src/text_file_reader.h

@@ -25,7 +25,6 @@
 namespace LAMMPS_NS
 {
   class TextFileReader {
-    std::string filename;
     std::string filetype;
     static constexpr int MAXLINE = 1024;
     char line[MAXLINE];
@@ -35,6 +34,8 @@ namespace LAMMPS_NS
     bool ignore_comments; //!< Controls whether comments are ignored
 
     TextFileReader(const std::string &filename, const std::string &filetype);
+    TextFileReader(FILE *fp, const std::string &filetype);
+
     ~TextFileReader();
 
     void skip_line();