[PHP源码阅读]explode和implode函数，explodeimplode

explode和implode函数主要用作字符串-数组的操作，比如获取一段参数后根据某个字符分割字符串，或者将一个数组的结果使用一个字符合并成一个字符串输出。在PHP中经常会用到这两个函数，因此有必要了解一下其原理。

explode

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

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返回由字符串组成的数组，每个元素都是string的一个子串，被字符串$delimiter作为边界点分割出来。

$limit

如果设置了$limit，且为正数，则返回的数组最多包含$limit个元素，最后的那个元素将包含$string的剩余部分。

如果$limit是负数，则返回除了最后的-$limit个元素外的所有元素。

如果$limit是0，则会被当做1。

$delimiter

如果$delimiter为空，则函数返回FALSE。如果delimiter不在string中，且$limit为负数，则返回空数组。

核心源码

    <span>//</span><span> 如果delimiter为空字符串，返回FALSE</span>
    <span>if</span> (delim_len == <span>0</span><span>) {
        php_error_docref(NULL TSRMLS_CC, E_WARNING, </span><span>"</span><span>Empty delimiter</span><span>"</span><span>);
        RETURN_FALSE;
    }

    </span><span>//</span><span> 初始化返回的数组</span>
<span>    array_init(return_value);

    </span><span>if</span> (str_len == <span>0</span><span>) {
          </span><span>if</span> (limit >= <span>0</span><span>) {
              </span><span>//</span><span> 如果字符串为空且limit大于等于0，则返回一个包含空字符串的数组，注意此处sizeof("") == 1</span>
            add_next_index_stringl(return_value, <span>""</span>, <span>sizeof</span>(<span>""</span>) - <span>1</span>, <span>1</span><span>);
        }
        </span><span>return</span><span>;
    }

    </span><span>//</span><span> 初始化zstr和zdelim的字符串变量</span>
    ZVAL_STRINGL(&zstr, str, str_len, <span>0</span><span>);
    ZVAL_STRINGL(</span>&zdelim, delim, delim_len, <span>0</span><span>);
    </span><span>if</span> (limit > <span>1</span><span>) {
        </span><span>//</span><span> limit大于1，limit默认是LONG_MAX</span>
        php_explode(&zdelim, &<span>zstr, return_value, limit);
    } </span><span>else</span> <span>if</span> (limit < <span>0</span><span>) {
        </span><span>//</span><span> limit 为负数</span>
        php_explode_negative_limit(&zdelim, &<span>zstr, return_value, limit);
    } </span><span>else</span><span> {
        </span><span>//</span><span> limit为0，被当作1处理，返回整个字符串，add_index_stringl函数将str追加到数组return_value中</span>
        add_index_stringl(return_value, <span>0</span>, str, str_len, <span>1</span><span>);
    }</span>

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处理完特殊情况和初始化变量后，就调用php_explode/php_explode_negative_limit函数进行下一步处理。下面是php_explode函数的源码

php_explode

<span>　　endp </span>= Z_STRVAL_P(str) +<span> Z_STRLEN_P(str);

    </span><span>//</span><span> p1指向字符串的开始</span>
    p1 =<span> Z_STRVAL_P(str);
    </span><span>//</span><span> p2指向第一个分隔符的位置 ，找出分隔符位置主要用的是php_memnstr函数</span>
    p2 =<span> php_memnstr(Z_STRVAL_P(str), Z_STRVAL_P(delim), Z_STRLEN_P(delim), endp);

    </span><span>if</span> (p2 ==<span> NULL) {
        </span><span>//</span><span> p2为NULL表示找不到分隔符，直接返回整个字符串</span>
        add_next_index_stringl(return_value, p1, Z_STRLEN_P(str), <span>1</span><span>);
    } </span><span>else</span><span> {
        </span><span>do</span><span> {
            </span><span>//</span><span> 将p1添加到return_value数组中 ，移动到下一个分隔符的位置</span>
            add_next_index_stringl(return_value, p1, p2 - p1, <span>1</span><span>);
            p1 </span>= p2 +<span> Z_STRLEN_P(delim);
        } </span><span>while</span> ((p2 = php_memnstr(p1, Z_STRVAL_P(delim), Z_STRLEN_P(delim), endp)) != NULL &&
                 --limit > <span>1</span><span>);

        </span><span>//</span><span> 将最后一个值追加到return_value</span>
        <span>if</span> (p1 <=<span> endp)
            add_next_index_stringl(return_value, p1, endp</span>-p1, <span>1</span><span>);
    }</span>

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实现时调用了add_next_index_stringl将得到的每个字符串添加到数组return_value中。add_next_index_string是此功能的核心函数。

ZEND_API <span>int</span> add_next_index_stringl(zval *arg, <span>const</span> <span>char</span> *str, <span>uint</span> length, <span>int</span><span> duplicate) 
{
    zval </span>*<span>tmp;

    MAKE_STD_ZVAL(tmp);
    ZVAL_STRINGL(tmp, str, length, duplicate);

    </span><span>return</span> zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp, <span>sizeof</span>(zval *<span>), NULL);
}</span>

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add_next_index_stringl函数调用zend_hash_next_index_insert函数将str插入到数组中。再看看php_explode_negative_limit函数的源码

php_explode_negative_limit

<span>　　//</span><span> 如果delimiter不在string中，且limit为负数，什么都不做，返回空的array，p2为NULL表示delimiter不在string中</span>
    <span>if</span> (p2 ==<span> NULL) {
        </span><span>/*<br />　　　　 如果limit <= -1，那么什么都不做，因此如果只有一个字符串，那么- 1 + (limit) <= 0<br />　　　　 返回空数组</span><span>*/</span><span>
    } </span><span>else</span><span> {
        </span><span>int</span> allocated = EXPLODE_ALLOC_STEP, found = <span>0</span><span>;
        </span><span>long</span><span> i, to_return;
        </span><span>char</span> **positions = emalloc(allocated * <span>sizeof</span>(<span>char</span> *<span>));
        </span><span>//</span><span> 第一个单词的位置</span>
        positions[found++] =<span> p1;
        </span><span>do</span><span> {
            </span><span>if</span> (found >=<span> allocated) {
                allocated </span>= found + EXPLODE_ALLOC_STEP;<span>/*</span><span> 保证有足够的内存空间 </span><span>*/</span><span>
                positions </span>= erealloc(positions, allocated*<span>sizeof</span>(<span>char</span> *<span>));
            }
            </span><span>//</span><span> positions保存每个单词的起始位置</span>
            positions[found++] = p1 = p2 +<span> Z_STRLEN_P(delim);
        } </span><span>while</span> ((p2 = php_memnstr(p1, Z_STRVAL_P(delim), Z_STRLEN_P(delim), endp)) !=<span> NULL);

        </span><span>//</span><span> to_return 是return_value的数量，其实等于found - |limit|</span>
        to_return = limit +<span> found;
        </span><span>/*</span><span> limit至少是-1，因此不需要边界检查：i永远小于found </span><span>*/</span>
        <span>for</span> (i = <span>0</span>;i < to_return;i++) { <span>/*</span><span> 这个检查是检查to_return大于0 </span><span>*/</span><span>
            add_next_index_stringl(return_value, positions[i],
                    (positions[i</span>+<span>1</span>] - Z_STRLEN_P(delim)) -<span> positions[i],
                    </span><span>1</span><span>
                );
        }
        efree(positions);
    }</span>

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php_explode_negative_limit也是跟php_implode类似的操作，找到分隔的字符串之后，调用add_next_index_string函数将limit + found个字符串添加到return_value数组中。

implode

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

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将一个一维数组的值转换为字符串

implode函数可以接收两种参数顺序。

核心代码

<span>if</span> (arg2 ==<span> NULL) {
        </span><span>//</span><span> 第二个参数为空，第一个参数必须为数组</span>
        <span>if</span> (Z_TYPE_PP(arg1) !=<span> IS_ARRAY) {
            php_error_docref(NULL TSRMLS_CC, E_WARNING, </span><span>"</span><span>Argument must be an array</span><span>"</span><span>);
            </span><span>return</span><span>;
        }

        MAKE_STD_ZVAL(delim);
</span><span>#define</span> _IMPL_EMPTY ""
        <span>//</span><span> 默认使用""连接</span>
        ZVAL_STRINGL(delim, _IMPL_EMPTY, <span>sizeof</span>(_IMPL_EMPTY) - <span>1</span>, <span>0</span><span>);

        SEPARATE_ZVAL(arg1);
        arr </span>= *<span>arg1;
    } </span><span>else</span><span> {
        </span><span>//</span><span> 根据参数类型设置参数的值</span>
        <span>if</span> (Z_TYPE_PP(arg1) ==<span> IS_ARRAY) {
            arr </span>= *<span>arg1;
            convert_to_string_ex(arg2);
            delim </span>= *<span>arg2;
        } </span><span>else</span> <span>if</span> (Z_TYPE_PP(arg2) ==<span> IS_ARRAY) {
            arr </span>= *<span>arg2;
            convert_to_string_ex(arg1);
            delim </span>= *<span>arg1;
        } </span><span>else</span><span> {
            php_error_docref(NULL TSRMLS_CC, E_WARNING, </span><span>"</span><span>Invalid arguments passed</span><span>"</span><span>);
            </span><span>return</span><span>;
        }
    }

    </span><span>//</span><span> 调用php_implode函数进行转换</span>
    php_implode(delim, arr, return_value TSRMLS_CC);

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在底层实现中，implode函数处理好参数之后就调用php_implode函数进行转换。

php_implode

<span>　　//</span><span> 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</span>
    <span>while</span> (zend_hash_get_current_data_ex(Z_ARRVAL_P(arr), (<span>void</span> **) &tmp, &pos) ==<span> SUCCESS) {
        </span><span>switch</span> ((*tmp)-><span>type) {
            </span><span>case</span><span> IS_STRING:
                smart_str_appendl(</span>&<span>implstr, Z_STRVAL_PP(tmp), Z_STRLEN_PP(tmp));
                </span><span>break</span><span>;

            </span><span>case</span><span> IS_LONG: {
                </span><span>char</span> stmp[MAX_LENGTH_OF_LONG + <span>1</span><span>];
                str_len </span>= slprintf(stmp, <span>sizeof</span>(stmp), <span>"</span><span>%ld</span><span>"</span><span>, Z_LVAL_PP(tmp));
                smart_str_appendl(</span>&<span>implstr, stmp, str_len);
            }
                </span><span>break</span><span>;

            </span><span>case</span><span> IS_BOOL:
                </span><span>if</span> (Z_LVAL_PP(tmp) == <span>1</span><span>) {
                    smart_str_appendl(</span>&implstr, <span>"</span><span>1</span><span>"</span>, <span>sizeof</span>(<span>"</span><span>1</span><span>"</span>)-<span>1</span><span>);
                }
                </span><span>break</span><span>;

            </span><span>case</span><span> IS_NULL:
                </span><span>break</span><span>;

            </span><span>case</span><span> IS_DOUBLE: {
                </span><span>char</span> *<span>stmp;
                str_len </span>= spprintf(&stmp, <span>0</span>, <span>"</span><span>%.*G</span><span>"</span>, (<span>int</span><span>) EG(precision), Z_DVAL_PP(tmp));
                smart_str_appendl(</span>&<span>implstr, stmp, str_len);
                efree(stmp);
            }
                </span><span>break</span><span>;

            </span><span>case</span><span> IS_OBJECT: {
                </span><span>int</span><span> copy;
                zval expr;
                zend_make_printable_zval(</span>*tmp, &expr, &<span>copy);
                smart_str_appendl(</span>&<span>implstr, Z_STRVAL(expr), Z_STRLEN(expr));
                </span><span>if</span><span> (copy) {
                    zval_dtor(</span>&<span>expr);
                }
            }
                </span><span>break</span><span>;

            </span><span>default</span><span>:
                tmp_val </span>= **<span>tmp;
                zval_copy_ctor(</span>&<span>tmp_val);
                convert_to_string(</span>&<span>tmp_val);
                smart_str_appendl(</span>&<span>implstr, Z_STRVAL(tmp_val), Z_STRLEN(tmp_val));
                zval_dtor(</span>&<span>tmp_val);
                </span><span>break</span><span>;

        }

        </span><span>//</span><span> 添加glue字符</span>
        <span>if</span> (++i !=<span> numelems) {
            smart_str_appendl(</span>&<span>implstr, Z_STRVAL_P(delim), Z_STRLEN_P(delim));
        }
        zend_hash_move_forward_ex(Z_ARRVAL_P(arr), </span>&<span>pos);
    }
    </span><span>//</span><span> 在尾部添加字符0</span>
    smart_str_0(&implstr);

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可以看到，php_implode函数遍历数组的每一个元素，判断其类型，并进行必要的类型转换，然后调用smart_str_appendl函数将值追加到字符串中。smart_str_appendl是implode实现代码中的核心函数。

smart_str_appendl

<span>#define</span> smart_str_appendl(dest, src, len) \<span>
    smart_str_appendl_ex((dest), (src), (len), </span><span>0</span><span>)

</span><span>#define</span> smart_str_appendl_ex(dest, src, nlen, what) do {            \<span>
    register size_t __nl;                                            \
    smart_str </span>*__dest = (smart_str *<span>) (dest);                        \
                                                                    \
    smart_str_alloc4(__dest, (nlen), (what), __nl);                    \
    memcpy(__dest</span>->c + __dest-><span>len, (src), (nlen));                    \
    __dest</span>->len =<span> __nl;                                                \
} </span><span>while</span> (<span>0</span>)

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smart_str_appendl_ex主要调用memcpy函数进行字符串复制。

原创文章，文笔有限，才疏学浅，文中若有不正之处，万望告知。

如果本文对你有帮助，点个推荐吧，谢谢^_^。

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