From 79b05d5e259fc2a83075cc7d8058b13b810da00b Mon Sep 17 00:00:00 2001
From: Rokas Kupstys <19151258+rokups@users.noreply.github.com>
Date: Fri, 17 Jun 2022 17:09:25 +0300
Subject: [PATCH] Fix freed memory read error in AddTicksTime(). Invalid read
 occurred when LabelTickTime() resizes ticks.TextBuffer while last_major held
 pointer pointing into old now freed buffer. (#365)

Fixed a warning about condition depending on uninitialized ImPlotLegend::PreviousLocation.
---
 implot.cpp        | 12 ++++++------
 implot_internal.h |  2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/implot.cpp b/implot.cpp
index aea9dba..ec6dcdb 100644
--- a/implot.cpp
+++ b/implot.cpp
@@ -1154,7 +1154,7 @@ void AddTicksTime(const ImPlotRange& range, float plot_width, ImPlotTickCollecti
     // maximum allowable density of labels
     const float max_density = 0.5f;
     // book keeping
-    const char* last_major  = NULL;
+    int last_major_offset = -1;
     if (unit0 != ImPlotTimeUnit_Yr) {
         // pixels per major (level 1) division
         const float pix_per_major_div = plot_width / (float)(range.Size() / TimeUnitSpans[unit1]);
@@ -1181,11 +1181,11 @@ void AddTicksTime(const ImPlotRange& range, float plot_width, ImPlotTickCollecti
                 // major level 1 tick
                 ImPlotTick tick_maj(t1.ToDouble(),true,true);
                 tick_maj.Level = 1;
-                LabelTickTime(tick_maj,ticks.TextBuffer,t1, last_major == NULL ? fmtf : fmt1);
+                LabelTickTime(tick_maj,ticks.TextBuffer,t1, last_major_offset < 0 ? fmtf : fmt1);
                 const char* this_major = ticks.TextBuffer.Buf.Data + tick_maj.TextOffset;
-                if (last_major && TimeLabelSame(last_major,this_major))
+                if (last_major_offset >= 0 && TimeLabelSame(ticks.TextBuffer.Buf.Data + last_major_offset, this_major))
                     tick_maj.ShowLabel = false;
-                last_major = this_major;
+                last_major_offset = tick_maj.TextOffset;
                 ticks.Append(tick_maj);
             }
             // add minor ticks up until next major
@@ -1198,11 +1198,11 @@ void AddTicksTime(const ImPlotRange& range, float plot_width, ImPlotTickCollecti
                         tick.Level =  0;
                         LabelTickTime(tick,ticks.TextBuffer,t12,fmt0);
                         ticks.Append(tick);
-                        if (last_major == NULL && px_to_t2 >= fmt0_width && px_to_t2 >= (fmt1_width + fmtf_width) / 2) {
+                        if (last_major_offset < 0 && px_to_t2 >= fmt0_width && px_to_t2 >= (fmt1_width + fmtf_width) / 2) {
                             ImPlotTick tick_maj(t12.ToDouble(),true,true);
                             tick_maj.Level = 1;
                             LabelTickTime(tick_maj,ticks.TextBuffer,t12,fmtf);
-                            last_major = ticks.TextBuffer.Buf.Data + tick_maj.TextOffset;
+                            last_major_offset = tick_maj.TextOffset;
                             ticks.Append(tick_maj);
                         }
                     }
diff --git a/implot_internal.h b/implot_internal.h
index 12b94be..e1f1acf 100644
--- a/implot_internal.h
+++ b/implot_internal.h
@@ -887,7 +887,7 @@ struct ImPlotLegend
         Flags        = PreviousFlags = ImPlotLegendFlags_None;
         CanGoInside  = true;
         Hovered      = Held = false;
-        Location     = ImPlotLocation_NorthWest;
+        Location     = PreviousLocation = ImPlotLocation_NorthWest;
     }
 
     void Reset() { Indices.shrink(0); Labels.Buf.shrink(0); }