_CP_field_store is equivalent to the result[string2, expression1, expression2] = string1 BASIC statement.
int _CP_field_store(CPSTR** result, CPSTR* string1, CPSTR* string2, int expression1, int expression2)
This function returns -1 if an error occurs. The error code is contained in _CP_errno.
/* Prints "zdhidz" */
CPSTR * s = _CP_mkstr("zdabdz");
CPSTR * t = _CP_mkstr("d");
CPSTR * u = _CP_mkstr("hi");
_CP_field_store(&s,u,t,2,1);
_CP_print(s);