[PHP source code reading] explode and implode functions, explodeimplode_PHP tutorial

[PHP source code reading] explode and implode functions, explodeimplode

explode and implode functions are mainly used for conversion operations between strings and arrays, such as obtaining a parameter and then according to a certain Character splits the string, or combines the result of an array into a string output using one character. These two functions are often used in PHP, so it is necessary to understand their principles.

explode

<p>array explode ( string $delimiter, string $string, [ , $limit ] )</p>

The function returns an array composed of strings. Each element is a substring of string, separated by the string $delimiter as a boundary point.

Parameter description

limit

If $limit is set and is a positive number, the returned array contains at most $limit elements, and the last element will contain the remainder of $string.

If $limit is a negative number, return all elements except the last -$limit elements.

If $limit is 0, it will be treated as 1.

delimiter

If $delimiter is empty, the function returns FALSE. If delimiter is not in string and $limit is a negative number, an empty array is returned.

Run the example

<span>$str</span> = 'hello,world,heiheihei,php';

Let’s first look at the situation without setting a limit

<span>$arr</span> = <span>explode</span>(',', <span>$str</span><span>);
</span><span>print_r</span>(<span>$arr</span>);

When limit is a positive number, limit is set to 1, and a maximum of 1 element is returned.

<span>$arr</span> = <span>explode</span>(',', <span>$str</span>, 1<span>);
</span><span>print_r</span>(<span>$arr</span>);

limit is a negative number, limit is -1, and all elements except the last element are returned.

<span>$arr</span> = <span>explode</span>(',', <span>$str</span>, -1<span>);
</span><span>print_r</span>(<span>$arr</span>);

limit is 0 and is treated as 1.

<span>$arr</span> = <span>explode</span>(',', <span>$str</span>, 0<span>);
</span><span>print_r</span>(<span>$arr</span>);

explode execution steps

<p>1、接收参数，处理参数为空的情况</p>
<p>2、创建函数中使用的局部变量</p>
<p>3、根据limit的值调用不同的函数分隔字符串</p>

The core implementation of the explode function is the php_explode function. The following is the execution flow chart of this function:

if (p2 == NULL) { // If the separator is not found, the entire string is returned directly add_next_index_stringl(return_value, p1, Z_STRLEN_P(str), 1); } else { do { // Add p1 to the return_value array add_next_index_stringl(return_value, p1, p2 - p1, 1); p1 = p2 Z_STRLEN_P(delim); } while ((p2 = php_memnstr(p1, Z_STRVAL_P(delim), Z_STRLEN_P(delim), endp)) != NULL && --limit > 1); // Add the last value to return_value if (p1 <= endp) add_next_index_stringl(return_value, p1, endp-p1, 1); }

Source code interpretation

sizeof("") == 0. sizeof has two uses, sizeof(typename) and sizeof(expression). When the parameter is typename, that is, the type name, sizeof returns the size of the object corresponding to the type; when the parameter is expression expression, sizeof calculates the size of the object corresponding to the return type of the expression. Here, "" is an expression. sizeof calculates the space allocated to "" by the compiler during compilation. At this time, it must be included

If limit is not set, the default value of limit is

LONG_MAX. In the php.h file, LONG_MAX is defined as 2147483647L.

In the implementation, if the limit is greater than 1, the

php_explode function is called; if the limit is less than 0, the php_explode_negative_limit function is called; if the limit is equal to 0, it is treated as 1. At this time, call the add_index_stringl function to add str to the array return_value.

When searching for the delimiter delimiter, the

php_memnstr function was called
php_memnstr(Z_STRVAL_P(str), Z_STRVAL_P(delim), Z_STRLEN_P(delim), endp); And php_memnstr is the macro definition of
zend_memnstr, which is implemented in zend_memnstr, so memchr in C is actually called to find the character delimiter.

After finding the position of the separator, call the

add_next_index_stringl function to insert the separated string into the return array.

implode

<p>string implode ( string $glue, array $pieces )<br />string implode ( array $pieces )</p>

Convert the value of a one-dimensional array to a string

Parameter description

The implode function can receive two parameter orders. Also, if the first parameter is an array and the second parameter is empty, the second parameter is the default value ''. This function can be seen as the reverse process of explode.

Of course, use the documented order to avoid confusion.

Run the example

<span>$arr</span> = <span>array</span>('hello', 'world');

Parameters in document order

<span>$str</span> = <span>implode</span>('-&lsquo;, $arr);// 输出"hello-world"

The first parameter is an array

<span>$str</span> = <span>implode</span>(<span>$arr</span><span>); // 输出"helloworld"
</span><span>$str</span> = <span>implode</span>(<span>$arr</span>, '-'); // 输出"hello-world"

implode执行步骤

<p>1、接收参数并赋值<br />2、如果第二个参数为空，则判断第一个参数的类型是否为数组，如果不是，则报错。否则，则使用""对glue赋值，使用其作为连接符。<br />3、如果第二个参数不为空，那么，如果第一个参数是数组类型，则将第二个参数转换成字符串类型；否则，如果第二个参数是数组类型，则将第一个参数转换成字符串类型。<br />4、调用php_implode函数做字符串的连接。</p>

在implode函数设置完参数之后，底层就调用php_implode函数进行字符串连接，php_implode函数的执行流程图如下：

// 遍历数组的每一个元素，判断其类型，然后调用smart_str_appendl函数将值追加到字符串中 while (zend_hash_get_current_data_ex(Z_ARRVAL_P(arr), (void **) &tmp, &pos) == SUCCESS) { switch ((*tmp)->type) { case IS_STRING: smart_str_appendl(&implstr, Z_STRVAL_PP(tmp), Z_STRLEN_PP(tmp)); break; case IS_LONG: { char stmp[MAX_LENGTH_OF_LONG + 1]; str_len = slprintf(stmp, sizeof(stmp), "%ld", Z_LVAL_PP(tmp)); smart_str_appendl(&implstr, stmp, str_len); } break; case IS_BOOL: if (Z_LVAL_PP(tmp) == 1) { smart_str_appendl(&implstr, "1", sizeof("1")-1); } break; case IS_NULL: break; case IS_DOUBLE: { char *stmp; str_len = spprintf(&stmp, 0, "%.*G", (int) EG(precision), Z_DVAL_PP(tmp)); smart_str_appendl(&implstr, stmp, str_len); efree(stmp); } break; case IS_OBJECT: { int copy; zval expr; zend_make_printable_zval(*tmp, &expr, &copy); smart_str_appendl(&implstr, Z_STRVAL(expr), Z_STRLEN(expr)); if (copy) { zval_dtor(&expr); } } break; default: tmp_val = **tmp; zval_copy_ctor(&tmp_val); convert_to_string(&tmp_val); smart_str_appendl(&implstr, Z_STRVAL(tmp_val), Z_STRLEN(tmp_val)); zval_dtor(&tmp_val); break; } // 添加glue字符 if (++i != numelems) { smart_str_appendl(&implstr, Z_STRVAL_P(delim), Z_STRLEN_P(delim)); } zend_hash_move_forward_ex(Z_ARRVAL_P(arr), &pos); } // 在尾部添加结束字符0 smart_str_0(&implstr);

 

源码解读

php_implode会逐个获取数组里面的内容，然后判断每个元素的类型，再做必要的数据类型转换之后，调用smart_str_appendl函数将值追加到返回的字符串后面。最后，还要在字符串后面加上结束符，这是个必须的操作，以后编程时也应注意。

smart_str_appendl是函数smart_str_appendl_ex的宏定义，该函数调用了memcpy做字符串的复制。

小结

原创文章，文笔有限，才疏学浅，文中若有不正之处，万望告知。

暂且写这么多吧，还有更多的优化和PHP源码中常用的函数，将会在以后的源码阅读中慢慢讲述。

如果本文对你有帮助，请点下推荐吧，谢谢^_^

 

最后，我在github有对PHP源码更详细的注解。感兴趣的可以围观一下，给个star。PHP5.4源码注解。

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