Both mistakes might cause memory corruptions and segfaults:
1)
char *str;
long str_len; 
zend_parse_parameters(ZEND_NUM_ARGS(), "s", &str, &str_len)

2)
int num; 
zend_parse_parameters(ZEND_NUM_ARGS(), "l", &num)

上面的例子应该改成：

int str_len; ==> size_t str_len;

这样上述例子在php7下才能正常运行。

就这样开始了第一个扩展程序。

关于zend_parse_parameters这个函数的，以下的官方文档内容有介绍，读着很抽象，结合一两个例子就明白了这个取参数的函数的定义：

Type specifiers
---------------
The following list shows the type specifier, its meaning and the parameter 
types that need to be passed by address. All passed parameters are set
if the PHP parameter is non optional and untouched if optional and the 
parameter is not present. The only exception is O where the zend_class_entry*
has to be provided on input and is used to verify the PHP parameter is an 
instance of that class.

a - array (zval*)
A - array or object (zval*)
b - boolean (zend_bool)
C - class (zend_class_entry*)
d - double (double)
f - function or array containing php method call info (returned as 
zend_fcall_info and zend_fcall_info_cache)
h - array (returned as HashTable*)
H - array or HASH_OF(object) (returned as HashTable*)
l - long (zend_long)
L - long, limits out-of-range numbers to LONG_MAX/LONG_MIN (zend_long, ZEND_LONG_MAX/ZEND_LONG_MIN)
o - object of any type (zval*)
O - object of specific type given by class entry (zval*, zend_class_entry)
p - valid path (string without null bytes in the middle) and its length (char*, size_t)
P - valid path (string without null bytes in the middle) as zend_string (zend_string*)
r - resource (zval*)
s - string (with possible null bytes) and its length (char*, size_t)
S - string (with possible null bytes) as zend_string (zend_string*)
z - the actual zval (zval*)
* - variable arguments list (0 or more)
+ - variable arguments list (1 or more)

The following characters also have a meaning in the specifier string:
| - indicates that the remaining parameters are optional, they
should be initialized to default values by the extension since they
will not be touched by the parsing function if they are not
passed to it.
/ - use SEPARATE_ZVAL_IF_NOT_REF() on the parameter it follows
! - the parameter it follows can be of specified type or NULL. If NULL is
passed and the output for such type is a pointer, then the output
pointer is set to a native NULL pointer.
For 'b', 'l' and 'd', an extra argument of type zend_bool* must be
passed after the corresponding bool*, zend_long* or double* arguments,
respectively. A non-zero value will be written to the zend_bool if a
PHP NULL is passed.