support utils::guesspath() also on Windows

src/utils.cpp

@@ -37,6 +37,15 @@
 #include <sys/syslimits.h>
 #endif
 
+// target Windows version is Windows 7 and later
+#if defined(_WIN32_WINNT)
+#undef _WIN32_WINNT
+#endif
+#define _WIN32_WINNT _WIN32_WINNT_WIN7
+#include <io.h>
+#include <windows.h>
+#endif
+
 /*! \file utils.cpp */
 
 /*
@@ -154,6 +163,9 @@ std::string utils::getsyserror()
 
 /** On Linux the folder /proc/self/fd holds symbolic links to the actual
  * pathnames associated with each open file descriptor of the current process.
+ * On macOS the same kind of information can be obtained using ``fcntl(fd,F_GETPATH,buf)``.
+ * On Windows we use ``GetFinalPathNameByHandleA()`` which is available with
+ * Windows Vista and later.
  *
  * This function is used to provide a filename with error messages in functions
  * where the filename is not passed as an argument, but the FILE * pointer.
@@ -174,6 +186,13 @@ const char *utils::guesspath(char *buf, int len, FILE *fp)
     strncpy(buf, filepath, len - 1);
   else
     strncpy(buf, "(unknown)", len - 1);
+#elif defined(_WIN32)
+  char filepath[MAX_PATH];
+  HANDLE h = (HANDLE) _get_osfhandle(_fileno(fp));
+  if (GetFinalPathNameByHandleA(h, filepath, PATH_MAX, FILE_NAME_NORMALIZED) > 0)
+    strncpy(buf, filepath, len - 1);
+  else
+    strncpy(buf, "(unknown)", len - 1);
 #else
   strncpy(buf, "(unknown)", len - 1);
 #endif

src/utils.h

@@ -408,7 +408,7 @@ namespace utils {
 
   /*! Try to detect pathname from FILE pointer.
    *
-   * Currently only supported on Linux and macOS, otherwise will report "(unknown)".
+   * Currently supported on Linux, macOS, and Windows, otherwise will report "(unknown)".
    *
    *  \param buf  storage buffer for pathname. output will be truncated if not large enough
    *  \param len  size of storage buffer. output will be truncated to this length - 1

unittest/utils/test_utils.cpp

@@ -722,7 +722,7 @@ TEST(Utils, guesspath)
 {
     char buf[256];
     FILE *fp = fopen("test_guesspath.txt", "w");
-#if defined(__linux__) || (__APPLE__)
+#if defined(__linux__) || defined(__APPLE__) || defined(_WIN32)
     const char *path = utils::guesspath(buf, sizeof(buf), fp);
     ASSERT_THAT(path, EndsWith("test_guesspath.txt"));
 #else