lua_getinfo

int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);

Returns information about a specific function or function invocation.

To get information about a function invocation, the parameter ar must be a valid activation record that was filled by a previous call to lua_getstack or given as argument to a hook (see lua_Hook).

To get information about a function you push it onto the stack and start the what string with the character '=>='. (In that case, lua_getinfo pops the function in the top of the stack.) For instance, to know in which line a function f was defined, you can write the following code:

     lua_Debug ar;
     lua_getfield(L, LUA_GLOBALSINDEX, "f");  /* get global 'f' */
     lua_getinfo(L, ">S", &ar);
     printf("%d\n", ar.linedefined);

Each character in the string what selects some fields of the structure ar to be filled or a value to be pushed on the stack:

'=n=': fills in the field name and namewhat;
'=S=': fills in the fields source, short_src, linedefined, lastlinedefined, and what;
'=l=': fills in the field currentline;
'=u=': fills in the field nups;
'=f=': pushes onto the stack the function that is running at the given level;
'=L=': pushes onto the stack a table whose indices are the numbers of the lines that are valid on the function. (A valid line is a line with some associated code, that is, a line where you can put a break point. Non-valid lines include empty lines and comments.)

This function returns 0 on error (for instance, an invalid option in what).