From 9ef5b8a061169f756a75d77e2712bf5bb4a07ecf Mon Sep 17 00:00:00 2001
From: Xavier Robin <xavalias-github@xavier.robin.name>
Date: Fri, 29 May 2026 15:25:27 +0200
Subject: [PATCH] Show error message upon error opening log file

---
 src/CifFile.C | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/CifFile.C b/src/CifFile.C
index ede03e5..5e0772b 100644
--- a/src/CifFile.C
+++ b/src/CifFile.C
@@ -17,8 +17,11 @@
 #include <stdexcept>
 #include <set>
 #include <algorithm>
+#include <cerrno>
+#include <cstring>
 
 #include "GenString.h"
+#include "Exceptions.h"
 #include "RcsbFile.h"
 #include "CifString.h"
 #include "regex.h"
@@ -306,6 +309,14 @@ int CifFile::DataChecking(CifFile& ref, const string& diagFileName,
     ofstream log;
     log.open(diagFileName.c_str(), ios::out | ios::app);
 
+    if (!log.is_open() || log.fail())
+    {
+        string msg = "Unable to open diagnostic log file \"" + diagFileName + "\"";
+        if (errno != 0)
+            msg += ": " + string(strerror(errno));
+        throw FileException(msg, "CifFile::DataChecking");
+    }
+
     vector<string> refBlockNames;
     ref.GetBlockNames(refBlockNames);
 
@@ -344,6 +355,14 @@ int CifFile::DataChecking(CifFile& ref, const string& diagFileName,
         }
     }
 
+    if (log.fail())
+    {
+        string msg = "Unable to write diagnostic log file \"" + diagFileName + "\"";
+        if (errno != 0)
+            msg += ": " + string(strerror(errno));
+        throw FileException(msg, "CifFile::DataChecking");
+    }
+
     if (RcsbFile::IsEmpty(log))
     {
         log.close();