From cd798164131099ba9fba54fd4b810c40ff337bfd Mon Sep 17 00:00:00 2001
From: Weiqun Zhang <weiqunzhang@lbl.gov>
Date: Thu, 22 Aug 2024 10:51:58 -0700
Subject: [PATCH] IOFormatSaver

Add a class that can be used to save and restore IO stream format in a RAII
way. Below is an example.

    auto& os = amrex::OutStream();
    auto old_fill = os.fill();
    auto old_flags = os.flags();
    auto old_precision = os.precision();
    auto old_width = os.width();

    {
        IOFormatSaver iofmtsaver(os);

        os << std::setfill('x');
        os << std::left;
        os << std::setprecision(4);
        os << std::setw(111);
    }

    AMREX_ALWAYS_ASSERT(old_fill == os.fill());
    AMREX_ALWAYS_ASSERT(old_flags == os.flags());
    AMREX_ALWAYS_ASSERT(old_precision == os.precision());
    AMREX_ALWAYS_ASSERT(old_width == os.width());
---
 Src/Base/AMReX_IOFormat.H       | 51 +++++++++++++++++++++++++++++++++
 Src/Base/AMReX_TinyProfiler.cpp | 10 +++++--
 Src/Base/AMReX_VisMF.cpp        |  8 ++----
 Src/Base/CMakeLists.txt         |  1 +
 Src/Base/Make.package           |  1 +
 5 files changed, 63 insertions(+), 8 deletions(-)
 create mode 100644 Src/Base/AMReX_IOFormat.H

diff --git a/Src/Base/AMReX_IOFormat.H b/Src/Base/AMReX_IOFormat.H
new file mode 100644
index 0000000000..e9a5597cb0
--- /dev/null
+++ b/Src/Base/AMReX_IOFormat.H
@@ -0,0 +1,51 @@
+#ifndef AMREX_IO_FORMAT_H_
+#define AMREX_IO_FORMAT_H_
+
+#include <ios>
+
+namespace amrex {
+
+/*
+ * \brief I/O stream format saver
+ *
+ * This class can be used to save and restore I/O stream format in a RAII
+ * way. It handles fill, fmtflag, precision, and width.
+ */
+template <class CharT, class Traits>
+class IOFormatSaver
+{
+public:
+    using BasicIos = std::basic_ios<CharT, Traits>;
+
+    explicit IOFormatSaver (BasicIos& ios)
+        : m_ios(&ios),
+          m_fill(ios.fill()),
+          m_flags(ios.flags()),
+          m_precision(ios.precision()),
+          m_width(ios.width())
+    {}
+
+    ~IOFormatSaver ()
+    {
+        m_ios->fill(m_fill);
+        m_ios->flags(m_flags);
+        m_ios->precision(m_precision);
+        m_ios->width(m_width);
+    }
+
+    IOFormatSaver (IOFormatSaver const&) = delete;
+    IOFormatSaver (IOFormatSaver &&) noexcept = delete;
+    IOFormatSaver& operator= (IOFormatSaver const&) = delete;
+    IOFormatSaver& operator= (IOFormatSaver &&) noexcept = delete;
+
+private:
+    BasicIos*                   m_ios;
+    CharT                       m_fill;
+    typename BasicIos::fmtflags m_flags;
+    std::streamsize             m_precision;
+    std::streamsize             m_width;
+};
+
+}
+
+#endif
diff --git a/Src/Base/AMReX_TinyProfiler.cpp b/Src/Base/AMReX_TinyProfiler.cpp
index db92274578..4360cf7671 100644
--- a/Src/Base/AMReX_TinyProfiler.cpp
+++ b/Src/Base/AMReX_TinyProfiler.cpp
@@ -10,6 +10,7 @@
 #include <AMReX_GpuDevice.H>
 #endif
 #include <AMReX_Print.H>
+#include <AMReX_IOFormat.H>
 
 #ifdef AMREX_USE_OMP
 #include <omp.h>
@@ -386,7 +387,6 @@ TinyProfiler::Finalize (bool bFlushing) noexcept
 
     std::ofstream ofs;
     std::ostream* os = nullptr;
-    std::streamsize oldprec = 0;
     if (ParallelDescriptor::IOProcessor()) {
         if (output_file.empty()) {
             os = &(amrex::OutStream());
@@ -399,6 +399,8 @@ TinyProfiler::Finalize (bool bFlushing) noexcept
         }
     }
 
+    IOFormatSaver iofmtsaver(amrex::OutStream());
+
     if (os)
     {
         os->precision(4);
@@ -438,8 +440,6 @@ TinyProfiler::Finalize (bool bFlushing) noexcept
             }
         }
     }
-
-    if(os) { os->precision(oldprec); }
 }
 
 void
@@ -593,6 +593,8 @@ TinyProfiler::PrintStats (std::map<std::string,Stats>& regstats, double dt_max,
 
     if (ParallelDescriptor::IOProcessor() && os)
     {
+        IOFormatSaver iofmtsaver(*os);
+
         *os << std::setfill(' ') << std::setprecision(4);
         int wt = 9;
 
@@ -876,6 +878,8 @@ TinyProfiler::PrintMemStats (std::map<std::string, MemStat>& memstats,
 
     if (allstatsstr.size() == 1 || !os) { return; }
 
+    IOFormatSaver iofmtsaver(*os);
+
     int lenhline = 0;
     for (auto i : maxlen) {
         lenhline += i;
diff --git a/Src/Base/AMReX_VisMF.cpp b/Src/Base/AMReX_VisMF.cpp
index 2b0ac6716d..f5f1430d59 100644
--- a/Src/Base/AMReX_VisMF.cpp
+++ b/Src/Base/AMReX_VisMF.cpp
@@ -1,6 +1,7 @@
 
 #include <AMReX_FabArrayUtility.H>
 #include <AMReX_FPC.H>
+#include <AMReX_IOFormat.H>
 #include <AMReX_ParmParse.H>
 #include <AMReX_Utility.H>
 #include <AMReX_VisMF.H>
@@ -277,9 +278,9 @@ operator<< (std::ostream        &os,
     // Up the precision for the Reals in m_min and m_max.
     // Force it to be written in scientific notation to match fParallel code.
     //
-    std::ios::fmtflags oflags = os.flags();
+    IOFormatSaver iofmtsaver(os);
     os.setf(std::ios::floatfield, std::ios::scientific);
-    int oldPrec = static_cast<int>(os.precision(16));
+    os.precision(17);
 
     os << hd.m_vers     << '\n';
     os << int(hd.m_how) << '\n';
@@ -327,9 +328,6 @@ operator<< (std::ostream        &os,
       }
     }
 
-    os.flags(oflags);
-    os.precision(oldPrec);
-
     if( ! os.good()) {
         amrex::Error("Write of VisMF::Header failed");
     }
diff --git a/Src/Base/CMakeLists.txt b/Src/Base/CMakeLists.txt
index 0436ad032e..1ee0b23612 100644
--- a/Src/Base/CMakeLists.txt
+++ b/Src/Base/CMakeLists.txt
@@ -97,6 +97,7 @@ foreach(D IN LISTS AMReX_SPACEDIM)
        AMReX_Print.H
        AMReX_IntConv.H
        AMReX_IntConv.cpp
+       AMReX_IOFormat.H
        # Index space -------------------------------------------------------------
        AMReX_Box.H
        AMReX_Box.cpp
diff --git a/Src/Base/Make.package b/Src/Base/Make.package
index b009ebf7d6..a8c1d0faaa 100644
--- a/Src/Base/Make.package
+++ b/Src/Base/Make.package
@@ -121,6 +121,7 @@ C$(AMREX_BASE)_headers += AMReX_ParReduce.H
 #
 C${AMREX_BASE}_headers += AMReX_ANSIEscCode.H AMReX_FabConv.H AMReX_FPC.H AMReX_Print.H AMReX_IntConv.H AMReX_VectorIO.H
 C${AMREX_BASE}_sources += AMReX_FabConv.cpp AMReX_FPC.cpp AMReX_IntConv.cpp AMReX_VectorIO.cpp
+C${AMREX_BASE}_headers += AMReX_IOFormat.H
 
 #
 # Index space.