[Numpy-discussion] Correct C string handling in the NumPy C API?

[Sturla Molden]

Here is an example:

NPY_NO_EXPORT NpyIter_IterNextFunc *
NpyIter_GetIterNext(NpyIter *iter, char **errmsg)
{
     npy_uint32 itflags = NIT_ITFLAGS(iter);
     int ndim = NIT_NDIM(iter);
     int nop = NIT_NOP(iter);

     if (NIT_ITERSIZE(iter) < 0) {
         if (errmsg == NULL) {
             PyErr_SetString(PyExc_ValueError, "iterator is too large");
         }
         else {
             *errmsg = "iterator is too large";
         }
         return NULL;
     }


After NpyIter_GetIterNext returns, *errmsg points to a local variable in 
a returned function.

Either I am wrong about C, or this code has undefied behavior...

My gutfeeling is that

    *errmsg = "iterator is too large";

puts the string "iterator is too large" on the stack and points *errmsg 
to the string.

Shouldn't this really be

    strcpy(*errmsg, "iterator is too large");

and then *errmsg should point to a char buffer allocated before 
NpyIter_GetIterNext is called?

Or will the statement

    *errmsg = "iterator is too large";

put the string on the stack in the calling C function?

Before I open an issue I will ask if my understanding of C is correct or 
not.

I am a bit confused here...

Regards,
Sturla