Added truncate flag (issue #1297)

include/spdlog/details/pattern_formatter-inl.h

@@ -39,47 +39,50 @@ public:
         : padinfo_(padinfo)
         , dest_(dest)
     {
-
-        if (padinfo_.width_ <= wrapped_size)
+        remaining_pad_ = static_cast<long>(padinfo.width_) - static_cast<long>(wrapped_size);
+        if (remaining_pad_ <= 0)
         {
-            total_pad_ = 0;
             return;
         }
 
-        total_pad_ = padinfo.width_ - wrapped_size;
         if (padinfo_.side_ == padding_info::left)
         {
-            pad_it(total_pad_);
-            total_pad_ = 0;
+            pad_it(remaining_pad_);
+            remaining_pad_ = 0;
         }
         else if (padinfo_.side_ == padding_info::center)
         {
-            auto half_pad = total_pad_ / 2;
-            auto reminder = total_pad_ & 1;
+            auto half_pad = remaining_pad_ / 2;
+            auto reminder = remaining_pad_ & 1;
             pad_it(half_pad);
-            total_pad_ = half_pad + reminder; // for the right side
+            remaining_pad_ = half_pad + reminder; // for the right side
         }
     }
 
     ~scoped_padder()
     {
-        if (total_pad_)
+        if (remaining_pad_ >= 0)
         {
-            pad_it(total_pad_);
+            pad_it(remaining_pad_);
+        }
+        else if (padinfo_.truncate_)
+        {
+            long new_size = static_cast<long>(dest_.size()) + remaining_pad_;
+            dest_.resize(static_cast<size_t>(new_size));
         }
     }
 
 private:
-    void pad_it(size_t count)
+    void pad_it(long count)
     {
         // count = std::min(count, spaces_.size());
-        assert(count <= spaces_.size());
+        // assert(count <= spaces_.size());
         fmt_helper::append_string_view(string_view_t(spaces_.data(), count), dest_);
     }
 
     const padding_info &padinfo_;
     memory_buf_t &dest_;
-    size_t total_pad_;
+    long remaining_pad_;
     string_view_t spaces_{"                                                                ", 64};
 };
 
@@ -1209,7 +1212,7 @@ SPDLOG_INLINE void pattern_formatter::handle_flag_(char flag, details::padding_i
     }
 }
 
-// Extract given pad spec (e.g. %8X)
+// Extract given pad spec (e.g. %8X, %=8X, %-8!X, %8!X, %=8!X, %-8!X, %+8!X)
 // Advance the given it pass the end of the padding spec found (if any)
 // Return padding.
 SPDLOG_INLINE details::padding_info pattern_formatter::handle_padspec_(std::string::const_iterator &it, std::string::const_iterator end)
@@ -1240,7 +1243,7 @@ SPDLOG_INLINE details::padding_info pattern_formatter::handle_padspec_(std::stri
 
     if (it == end || !std::isdigit(static_cast<unsigned char>(*it)))
     {
-        return padding_info{0, side};
+        return padding_info{}; // no padding if no digit found here
     }
 
     auto width = static_cast<size_t>(*it) - '0';
@@ -1249,7 +1252,20 @@ SPDLOG_INLINE details::padding_info pattern_formatter::handle_padspec_(std::stri
         auto digit = static_cast<size_t>(*it) - '0';
         width = width * 10 + digit;
     }
-    return details::padding_info{std::min<size_t>(width, max_width), side};
+
+    // search for the optional truncate marker '!'
+    bool truncate;
+    if (it != end && *it == '!')
+    {
+        truncate = true;
+        ++it;
+    }
+    else
+    {
+        truncate = false;
+    }
+
+    return details::padding_info{std::min<size_t>(width, max_width), side, truncate};
 }
 
 SPDLOG_INLINE void pattern_formatter::compile_pattern_(const std::string &pattern)

include/spdlog/details/pattern_formatter.h

@@ -29,17 +29,21 @@ struct padding_info
     };
 
     padding_info() = default;
-    padding_info(size_t width, padding_info::pad_side side)
+    padding_info(size_t width, padding_info::pad_side side, bool truncate)
         : width_(width)
         , side_(side)
+        , truncate_(truncate)
+        , enabled_(true)
     {}
 
     bool enabled() const
     {
-        return width_ != 0;
+        return enabled_;
     }
     const size_t width_ = 0;
     const pad_side side_ = left;
+    bool truncate_ = false;
+    bool enabled_ = false;
 };
 
 class flag_formatter