有关print_r函数与数组指针位置

[huq1402]

http://cn2.php.net/manual/en/function.print-r.php

Remember that print_r() will move the array pointer to the end. Use reset() to bring it back to beginning.

== Test Code Below ==

<?php
	$a=array("test1", "test2", "test3");
	echo current($a);
	$t=print_r($a, true);
	echo current($a);
?>

== Output ==

test1test1

测试表明使用print_r函数后，数组内部指针被移到起始元素位置了而不是末端，如何解释？

[Coder_Granger]

print_r的函数在php5.3.2中是这么定义的

PHP_FUNCTION(print_r)
{
        zval *var;
        zend_bool do_return = 0; 

        if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "z|b", &var, &do_return) == FAILURE) {
                RETURN_FALSE;
        }    

        if (do_return) {
                php_start_ob_buffer (NULL, 0, 1 TSRMLS_CC);
        }    

        zend_print_zval_r(var, 0 TSRMLS_CC);

        if (do_return) {
                php_ob_get_buffer (return_value TSRMLS_CC);
                php_end_ob_buffer (0, 0 TSRMLS_CC);
        } else {
                RETURN_TRUE;
        }    
}

可以看出，实际上干活的是zend_print_zval_r，是它输出了变量，追踪这个函数

ZEND_API void zend_print_zval_r(zval *expr, int indent TSRMLS_DC)
{
        zend_print_zval_r_ex(zend_write, expr, indent TSRMLS_CC);
}

实际上调用了zend_print_zval_r_ex，继续追踪

ZEND_API void zend_print_zval_r_ex(zend_write_func_t write_func, zval *expr, int indent TSRMLS_DC) /* {{{ */
{
        switch (Z_TYPE_P(expr)) {
                case IS_ARRAY:
                        ZEND_PUTS_EX("Array\n");
                        if (++Z_ARRVAL_P(expr)->nApplyCount>1) {
                                ZEND_PUTS_EX(" *RECURSION*");
                                Z_ARRVAL_P(expr)->nApplyCount--;
                                return;
                        }    
                        print_hash(write_func, Z_ARRVAL_P(expr), indent, 0 TSRMLS_CC);
                        Z_ARRVAL_P(expr)->nApplyCount--;
                        break;
                case IS_OBJECT:
                        {
                                HashTable *properties;
                                char *class_name = NULL;
                                zend_uint clen;
                                int is_temp;

                                if (Z_OBJ_HANDLER_P(expr, get_class_name)) {
                                        Z_OBJ_HANDLER_P(expr, get_class_name)(expr, &class_name, &clen, 0 TSRMLS_CC);
                                }
                                if (class_name) {
                                        ZEND_PUTS_EX(class_name);
                                } else {
                                        ZEND_PUTS_EX("Unknown Class");
                                }
                                ZEND_PUTS_EX(" Object\n");
                                if (class_name) {
                                        efree(class_name);
                                }
                                if ((properties = Z_OBJDEBUG_P(expr, is_temp)) == NULL) {
                                        break;
                                }
                                if (++properties->nApplyCount>1) {
                                        ZEND_PUTS_EX(" *RECURSION*");
                                        properties->nApplyCount--;
                                        return;
                                }
                                print_hash(write_func, properties, indent, 1 TSRMLS_CC);
                                properties->nApplyCount--;
                                if (is_temp) {
                                        zend_hash_destroy(properties);
                                        efree(properties);
                                }
                                break;
                        }
                default:
                        zend_print_zval_ex(write_func, expr, indent);
                        break;
        }
}

可见，输出数组时，实际上工作的是print_hash，继续追踪

static void print_hash(zend_write_func_t write_func, HashTable *ht, int indent, zend_bool is_object TSRMLS_DC) /* {{{ */
{
        zval **tmp;
        char *string_key;
        HashPosition iterator;
        ulong num_key;
        uint str_len;
        int i;

        for (i = 0; i < indent; i++) {
                ZEND_PUTS_EX(" ");
        }
        ZEND_PUTS_EX("(\n");
        indent += PRINT_ZVAL_INDENT;
        zend_hash_internal_pointer_reset_ex(ht, &iterator);
        while (zend_hash_get_current_data_ex(ht, (void **) &tmp, &iterator) == SUCCESS) {
                for (i = 0; i < indent; i++) {
                        ZEND_PUTS_EX(" ");
                }
                ZEND_PUTS_EX("[");
                switch (zend_hash_get_current_key_ex(ht, &string_key, &str_len, &num_key, 0, &iterator)) {
                        case HASH_KEY_IS_STRING:
                                if (is_object) {
                                        char *prop_name, *class_name;
                                        int mangled = zend_unmangle_property_name(string_key, str_len - 1, &class_name, &prop_name);

                                        ZEND_PUTS_EX(prop_name);
                                        if (class_name && mangled == SUCCESS) {
                                                if (class_name[0]=='*') {
                                                        ZEND_PUTS_EX(":protected");
                                                } else {
                                                        ZEND_PUTS_EX(":");
                                                        ZEND_PUTS_EX(class_name);
                                                        ZEND_PUTS_EX(":private");
                                                }
                                        }
                                } else {
                                        ZEND_WRITE_EX(string_key, str_len-1);
                                }
                                break;
                        case HASH_KEY_IS_LONG:
                                {
                                        char key[25];
                                        snprintf(key, sizeof(key), "%ld", num_key);
                                        ZEND_PUTS_EX(key);
                                }
                                break;
                }
                ZEND_PUTS_EX("] => ");
                zend_print_zval_r_ex(write_func, *tmp, indent+PRINT_ZVAL_INDENT TSRMLS_CC);
                ZEND_PUTS_EX("\n");
                zend_hash_move_forward_ex(ht, &iterator);
        }
        indent -= PRINT_ZVAL_INDENT;
        for (i = 0; i < indent; i++) {
                ZEND_PUTS_EX(" ");
        }
        ZEND_PUTS_EX(")\n");
}

重点是这两句，含义是把ht->pListHead赋值给iterator

HashPosition iterator;
zend_hash_internal_pointer_reset_ex(ht, &iterator);

综上，print_r输出数组时，根本没有用到数组的内部迭代器，因此用后无需reset

但是最好还是reset一下，因为老版本的php可能用到了内部迭代器，
用后不reset可能导致代码无法在老版本的php环境中运行。

应该是php的文档没有跟上代码，有些迟滞了，将来会更新的。

[床上等您]

学习了，帮顶接分。

[LuciferStar]

学习了！