Lua API evaluates variable name instead of value

Question

I'm using the Lua 5.2 C API. I am trying to get a function to accept a string variable or a string literal.

this code:

static int printTest(lua_State *L)
{   
    size_t lslen = NULL;
    const char *lsrc = lua_tolstring(L, 0, &lslen);
    printf("%s\n", lsrc);
}
/* ----- Registration array ----- */
static const luaL_Reg testhook[] = {
        {"printTest", printTest},
        {NULL, NULL} /* sentinel */
};    
/* ----- Registration function ----- */    
LUALIB_API int registerTestHookFunctions(lua_State *L)
{
    lua_newtable(L); 
    lua_setglobal(L, "hook"); 
    lua_getglobal(L, "hook"); 
    luaL_setfuncs(L, testhook, 0); 
    lua_settop(L, 0);
    return 0;
}

when run from Lua, will do this:

hook.printTest('hello')  -- prints 'hello'
a = 'hello'
hook.printTest(a) -- prints 'a'

I'm very new to Lua and using this documentation: http://www.lua.org/manual/5.2/manual.html and am not finding/understanding how to discern a variable from a literal. (There are no lua_isliteral() or lua_isvariable() methods, for example).

Puppy · Accepted Answer · 2012-05-22 14:33:55Z

5

You have passed a bad index to lua_tolstring. The reference manual clearly states that

0 is never an acceptable index.

You use negative indices for relative values, and positive indices for absolute values. Neither of those conditions is ever 0.

answered May 22, 2012 at 14:33

Puppy

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1 Comment

Paul Over a year ago

Sigh. Embarrassingly obvious now that I see it. Thanks.

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