Question

Using the Lua C-API is there an efficient way to concatenate two LuaL_Buffers? I’d rather not do any unnecessary memcopys and want the result consumed by luaL_pushresult(). The buffers contain embedded zeros so I can’t convert them to char arrays and use luaL_addstring(). It is acceptable to modify either buffer.

luaL_Buffer buf1;
luaL_Buffer buf2;
luaL_buffinit(L, &buf1);
luaL_buffinit(L, &buf2);  
luaL_addchar(&buf1, "a");
luaL_addchar(&buf2, "b");
luaL_addchar(&buf1, "\0");
luaL_addchar(&buf2, "\0");
luaL_pushresult(L, Want_this(&buf1, &buf2) ); // "a\0b\0" is now the Lua string 
                                              //  at the top of the stack

Answer 1

You could push buf2 onto the stack first, add it to buf1 (which pops it), then push buf1 onto the stack.

luaL_pushresult(L, &buf2); // push "b\0" onto the stack
luaL_addvalue(&buf1); // pop that string and add it to buf1
luaL_pushresult(L, &buf1); // push "a\0b\0" onto the stack