Call stack print (Win32\64 Vista+\VS2010

#include <Windows.h>
#include <DbgHelp.h> // need  DbgHelp32.lib
#include <string>

#define TRACE_MAX_STACK_FRAMES 1024
#define TRACE_MAX_FUNCTION_NAME_LENGTH 1024

template <typename I>
std::string n2hexstr(I w, size_t hex_len = sizeof(I)<<1)
{
    std::string rc(hex_len,'0');
    for (size_t i=0, j=(hex_len-1)*4 ; i<hex_len; ++i,j-=4)
        rc[i] = ((w>>j) & 0x0f)["0123456789ABCDEF"];
    return rc;
}

// Outputs current frames without (skip_frames+1) frames from top of stack stack.
// not usable for exceptions and uses CaptureStackBackTrace из Windows Vista SDK (default VS2010)
// might need StackWalk64 fore more details about stack.
static bool GetStackWalk( std::string &outWalk, USHORT skip_frames = 0)
{
    // RTTI for .pdb symbols. Might want this in global scope
    static struct SymServer {
        bool good;
        SymServer() : good(false) {
            // deferred load, allow 32bit, undecorate names.
            ::SymSetOptions( SYMOPT_DEFERRED_LOADS | SYMOPT_INCLUDE_32BIT_MODULES | SYMOPT_UNDNAME );
            // Microsoft symbol servers.
            good = ::SymInitialize( ::GetCurrentProcess(),
                NULL, //  user path to .pdb
                TRUE ) == TRUE;
        }
        ~SymServer() { ::SymCleanup( ::GetCurrentProcess() ); }
    } SymServerGuard;

    if(!SymServerGuard.good) return false;
    auto hProcess = ::GetCurrentProcess();

    // up to TRACE_MAX_STACK_FRAMES
    PVOID addrs[ TRACE_MAX_STACK_FRAMES ] = { };
    // 1st frame is GetStackWalk.
    USHORT usFrames = CaptureStackBackTrace( 1 + skip_frames, TRACE_MAX_STACK_FRAMES - skip_frames, addrs, NULL );

    outWalk.append("=== Stack backtrace:\n");

    for (long long i = 0; i < usFrames; i++) {
        // buffer for SYMBOL_INFO with string of 1024 bytes.
        ULONG64 buffer[ (sizeof( SYMBOL_INFO ) + TRACE_MAX_FUNCTION_NAME_LENGTH + sizeof( ULONG64 ) - 1) / sizeof( ULONG64 ) ] = { 0 };

        SYMBOL_INFO *info = new (buffer) SYMBOL_INFO;
        info->SizeOfStruct = sizeof( SYMBOL_INFO );
        info->MaxNameLen = TRACE_MAX_FUNCTION_NAME_LENGTH;

        DWORD64 displacement = 0;
        IMAGEHLP_LINE64 line =  { sizeof(IMAGEHLP_LINE64) };

        // frame number
        outWalk.append(std::to_string(i)).append( ". " );

        DWORD disp = 0;
        // Attempt to get information about the symbol and add it to our output parameter.
        if(::SymFromAddr( hProcess, DWORD64(addrs[ i ]), &displacement, info ))
        {
           // attempt to get line info, if it present
           if (::SymGetLineFromAddr64(hProcess, DWORD(addrs[ i ]), &disp, &line))
           {
               outWalk.append( info->Name, info->NameLen ).append(" : 0x").append(n2hexstr(line.Address))
                   .append("\n\t\"").append(line.FileName).append("\" line: ").append(std::to_string((long long)line.LineNumber))
                   .append(" + ").append(std::to_string((long long)disp));
           }
           else
           {
               outWalk.append( info->Name, info->NameLen );
           }
        }
        outWalk.append( "\n" );
    }

    return true;
}

// Test thing
struct S {
    S() {
    std::string s;
    GetStackWalk(s);

    std::cout  << s << std::endl;
    }
} s;