Replace kstream::to_string() - not just int, fix portability

See #8 (comment)

Fix #28,
close #39

CMakeLists.txt

@@ -19,6 +19,9 @@ set (HEADERS
     kaitai/kaitaistream.h
     kaitai/kaitaistruct.h
     kaitai/exceptions.h
+    # required by public header kaitai/kaitaistream.h, so I guess it must be included as well
+    # (see https://stackoverflow.com/a/61152762)
+    kaitai/detail/make_unsigned.h
 )
 
 set (SOURCES

kaitai/detail/make_unsigned.h

@@ -0,0 +1,19 @@
+#ifndef KAITAI_DETAIL_MAKE_UNSIGNED_H
+#define KAITAI_DETAIL_MAKE_UNSIGNED_H
+
+namespace kaitai {
+    // poor man's implementation of `std::make_unsigned` in pre-C++11 versions
+    // (https://stackoverflow.com/a/27577556)
+    //
+    // Don't use this externally. This is an internal implementation helper
+    // and may be removed at any time.
+    template<typename T> struct make_unsigned { typedef T type; };
+    template<> struct make_unsigned<char> { typedef unsigned char type; };
+    template<> struct make_unsigned<signed char> { typedef unsigned char type; };
+    template<> struct make_unsigned<short> { typedef unsigned short type; };
+    template<> struct make_unsigned<int> { typedef unsigned int type; };
+    template<> struct make_unsigned<long> { typedef unsigned long type; };
+    // `long long` is available only since C++11
+}
+
+#endif

kaitai/exceptions.h

@@ -60,7 +60,7 @@ class undecided_endianness_error: public kstruct_error {
 class validation_failed_error: public kstruct_error {
 public:
     validation_failed_error(const std::string what, kstream* io, const std::string src_path):
-        kstruct_error("at pos " + kstream::to_string(static_cast<int>(io->pos())) + ": validation failed: " + what, src_path),
+        kstruct_error("at pos " + kstream::to_string(io->pos()) + ": validation failed: " + what, src_path),
         m_io(io)
     {
     }

kaitai/kaitaistream.cpp

@@ -566,22 +566,6 @@ int kaitai::kstream::mod(int a, int b) {
     return r;
 }
 
-#include <stdio.h>
-std::string kaitai::kstream::to_string(int val) {
-    // if int is 32 bits, "-2147483648" is the longest string representation
-    //   => 11 chars + zero => 12 chars
-    // if int is 64 bits, "-9223372036854775808" is the longest
-    //   => 20 chars + zero => 21 chars
-    char buf[25];
-    int got_len = snprintf(buf, sizeof(buf), "%d", val);
-
-    // should never happen, but check nonetheless
-    if (got_len > sizeof(buf))
-        throw std::invalid_argument("to_string: integer is longer than string buffer");
-
-    return std::string(buf);
-}
-
 #include <algorithm>
 std::string kaitai::kstream::reverse(std::string val) {
     std::reverse(val.begin(), val.end());

kaitai/kaitaistream.h

@@ -8,6 +8,15 @@
 #include <sstream>
 #include <stdint.h>
 #include <sys/types.h>
+#include <algorithm>
+#include <limits>
+
+// https://stackoverflow.com/a/40512515
+#if __cplusplus >= 201103L || (defined(_MSC_VER) && _MSC_VER >= 1900)
+#define KAITAI_STREAM_H_CPP11_SUPPORT
+#else
+#include <kaitai/detail/make_unsigned.h>
+#endif
 
 namespace kaitai {
 
@@ -224,7 +233,34 @@ class kstream {
      * Should be used in place of std::to_string() (which is available only
      * since C++11) in older C++ implementations.
      */
-    static std::string to_string(int val);
+    template<typename I>
+#ifdef KAITAI_STREAM_H_CPP11_SUPPORT
+    // https://stackoverflow.com/a/27913885
+    typename std::enable_if<
+            std::is_integral<I>::value,
+            std::string
+    >::type
+#else
+    std::string
+#endif
+    static to_string(I val) {
+#ifdef KAITAI_STREAM_H_CPP11_SUPPORT
+        typedef typename std::make_unsigned<I>::type U;
+#else
+        typedef typename make_unsigned<I>::type U;
+#endif
+        // in theory, `digits10 + 3` would be enough (minus sign + leading digit
+        // + null terminator), but let's add a little more to be safe
+        char buf[std::numeric_limits<I>::digits10 + 5];
+        if (val < 0) {
+            buf[0] = '-';
+            // get absolute value without undefined behavior (https://stackoverflow.com/a/12231604)
+            unsigned_to_decimal<U>(-static_cast<U>(val), &buf[1]);
+        } else {
+            unsigned_to_decimal<U>(val, buf);
+        }
+        return std::string(buf);
+    }
 
     /**
      * Reverses given string `val`, so that the first character becomes the
@@ -258,6 +294,31 @@ class kstream {
     void init();
     void exceptions_enable() const;
 
+    template<typename U>
+#ifdef KAITAI_STREAM_H_CPP11_SUPPORT
+    typename std::enable_if<
+            std::is_integral<U>::value && std::is_unsigned<U>::value,
+            void
+    >::type
+#else
+    void
+#endif
+    static inline unsigned_to_decimal(U number, char *buffer) {
+        // Implementation from https://ideone.com/nrQfA8 by Alf P. Steinbach
+        // (see https://www.zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html#comment-1033931478)
+        if (number == 0) {
+            *buffer++ = '0';
+        } else {
+            char *p_first = buffer;
+            while (number != 0) {
+                *buffer++ = static_cast<char>('0' + number % 10);
+                number /= 10;
+            }
+            std::reverse(p_first, buffer);
+        }
+        *buffer = '\0';
+    }
+
     static const int ZLIB_BUF_SIZE = 128 * 1024;
 };