ENH: enable user to control re-writing of function object output file headers. See #1556

src/OpenFOAM/db/functionObjects/writeFile/writeFile.C

@@ -161,6 +161,7 @@ Foam::functionObjects::writeFile::writeFile(const writeFile& wf)
     filePtr_(),
     writePrecision_(wf.writePrecision_),
     writeToFile_(wf.writeToFile_),
+    updateHeader_(wf.updateHeader_),
     writtenHeader_(wf.writtenHeader_),
     useUserTime_(wf.useUserTime_),
     startTime_(wf.startTime_)
@@ -180,6 +181,7 @@ Foam::functionObjects::writeFile::writeFile
     fileName_(name),
     filePtr_(),
     writePrecision_(IOstream::defaultPrecision()),
+    updateHeader_(true),
     writeToFile_(writeToFile),
     writtenHeader_(false),
     useUserTime_(true),
@@ -214,6 +216,9 @@ bool Foam::functionObjects::writeFile::read(const dictionary& dict)
     writePrecision_ =
         dict.getOrDefault("writePrecision", IOstream::defaultPrecision());
 
+    updateHeader_ =
+        dict.lookupOrDefault("updateHeader", updateHeader_);
+
     // Only write on master
     writeToFile_ =
         Pstream::master() && dict.getOrDefault("writeToFile", writeToFile_);
@@ -248,6 +253,12 @@ bool Foam::functionObjects::writeFile::writeToFile() const
 }
 
 
+bool Foam::functionObjects::writeFile::canWriteHeader() const
+{
+    return writeToFile_ && (updateHeader_ || !writtenHeader_);
+}
+
+
 Foam::label Foam::functionObjects::writeFile::charWidth() const
 {
     return writePrecision_ + addChars;

src/OpenFOAM/db/functionObjects/writeFile/writeFile.H

@@ -82,6 +82,10 @@ protected:
         //- Flag to enable/disable writing to file
         bool writeToFile_;
 
+        //- Flag to update the header, e.g. on mesh changes.
+        //- Default is true.
+        bool updateHeader_;
+
         //- Flag to identify whether the header has been written
         bool writtenHeader_;
 
@@ -175,6 +179,9 @@ public:
         //- Flag to allow writing to file
         virtual bool writeToFile() const;
 
+        //- Flag to allow writing the header
+        virtual bool canWriteHeader() const;
+
         //- Return width of character stream output
         virtual label charWidth() const;
 

src/functionObjects/field/fieldValues/surfaceFieldValue/surfaceFieldValue.C

@@ -543,9 +543,9 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::update()
 void Foam::functionObjects::fieldValues::surfaceFieldValue::writeFileHeader
 (
     Ostream& os
-) const
+)
 {
-    if (operation_ != opNone)
+    if (canWriteHeader() && (operation_ != opNone))
     {
         writeCommented(os, "Region type : ");
         os << regionTypeNames_[regionType_] << " " << regionName_ << endl;
@@ -575,6 +575,8 @@ void Foam::functionObjects::fieldValues::surfaceFieldValue::writeFileHeader
 
         os  << endl;
     }
+
+    writtenHeader_ = true;
 }
 
 

src/functionObjects/field/fieldValues/surfaceFieldValue/surfaceFieldValue.H

@@ -529,7 +529,7 @@ protected:
 
 
         //- Output file header information
-        virtual void writeFileHeader(Ostream& os) const;
+        virtual void writeFileHeader(Ostream& os);
 
 
 public: