本文详细解析PHP中var_dump和echo的底层实现，通过查看源码，揭示两者在输出变量信息时的区别及原理，包括如何在var_dump中获取变量详细信息，以及echo如何通过zend引擎和fwrite进行输出。
在一个php群里有朋友提到 :
用 var_dump （$list）; 可以输出来内容，而 echo $list["name"]; 却不能输出 内容来，这是什么情况啊
这种问题的答案肯定要在源码里面找一找了
git回来了php-src 的master版本
查找函数php_var_dump，源码如下：
PHPAPI void php_var_dump(zval **struc, int level TSRMLS_DC) /* {{{ */
{
HashTable *myht;
const char *class_name;
zend_uint class_name_len;
int (*php_element_dump_func)(zval** TSRMLS_DC, int, va_list, zend_hash_key*);
int is_temp;
if (level > 1) {
php_printf("%*c", level - 1, ' ');
}
switch (Z_TYPE_PP(struc)) {
case IS_BOOL:
php_printf("%sbool(%s)\n", COMMON, Z_LVAL_PP(struc) ? "true" : "false");
break;
case IS_NULL:
php_printf("%sNULL\n", COMMON);
break;
case IS_LONG:
php_printf("%sint(%ld)\n", COMMON, Z_LVAL_PP(struc));
break;
case IS_DOUBLE:
php_printf("%sfloat(%.*G)\n", COMMON, (int) EG(precision), Z_DVAL_PP(struc));
break;
case IS_STRING:
php_printf("%sstring(%d) \"", COMMON, Z_STRLEN_PP(struc));
PHPWRITE(Z_STRVAL_PP(struc), Z_STRLEN_PP(struc));
PUTS("\"\n");
break;
case IS_ARRAY:
myht = Z_ARRVAL_PP(struc);
if (++myht->nApplyCount > 1) {
PUTS("*RECURSION*\n");
--myht->nApplyCount;
return;
}
php_printf("%sarray(%d) {\n", COMMON, zend_hash_num_elements(myht));
php_element_dump_func = php_array_element_dump;
is_temp = 0;
goto head_done;
case IS_OBJECT:
myht = Z_OBJDEBUG_PP(struc, is_temp);
if (myht && ++myht->nApplyCount > 1) {
PUTS("*RECURSION*\n");
--myht->nApplyCount;
return;
}
if (Z_OBJ_HANDLER(**struc, get_class_name)) {
Z_OBJ_HANDLER(**struc, get_class_name)(*struc, &class_name, &class_name_len, 0 TSRMLS_CC);
php_printf("%sobject(%s)#%d (%d) {\n", COMMON, class_name, Z_OBJ_HANDLE_PP(struc), myht ? zend_hash_num_elements(myht) : 0);
efree((char*)class_name);
} else {
php_printf("%sobject(unknown class)#%d (%d) {\n", COMMON, Z_OBJ_HANDLE_PP(struc), myht ? zend_hash_num_elements(myht) : 0);
}
php_element_dump_func = php_object_property_dump;
head_done:
if (myht) {
zend_hash_apply_with_arguments(myht TSRMLS_CC, (apply_func_args_t) php_element_dump_func, 1, level);
--myht->nApplyCount;
if (is_temp) {
zend_hash_destroy(myht);
efree(myht);
}
}
if (level > 1) {
php_printf("%*c", level-1, ' ');
}
PUTS("}\n");
break;
case IS_RESOURCE: {
const char *type_name = zend_rsrc_list_get_rsrc_type(Z_LVAL_PP(struc) TSRMLS_CC);
php_printf("%sresource(%ld) of type (%s)\n", COMMON, Z_LVAL_PP(struc), type_name ? type_name : "Unknown");
break;
}
default:
php_printf("%sUNKNOWN:0\n", COMMON);
break;
}
}对于每一种类型的变量都把具体得信息打印了出来
再看看echo，echo是由zend引擎来执行
void zend_do_echo(const znode *arg TSRMLS_DC) /* {{{ */
{
zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC);
opline->opcode = ZEND_ECHO;
SET_NODE(opline->op1, arg);
SET_UNUSED(opline->op2);
}
/* }}} */ZEND_VM_HANDLER(40, ZEND_ECHO, CONST|TMP|VAR|CV, ANY)
{
USE_OPLINE
zend_free_op free_op1;
zval *z;
SAVE_OPLINE();
z = GET_OP1_ZVAL_PTR(BP_VAR_R);
if (OP1_TYPE == IS_TMP_VAR && Z_TYPE_P(z) == IS_OBJECT) {
INIT_PZVAL(z);
}
zend_print_variable(z);
FREE_OP1();
CHECK_EXCEPTION();
ZEND_VM_NEXT_OPCODE();
}代码到这里就可以明白，echo是交给zend虚拟机了，再看看这个
ZEND_API int zend_print_variable(zval *var)
{
return zend_print_zval(var, 0);
}
ZEND_API int zend_print_zval(zval *expr, int indent) /* {{{ */
{
return zend_print_zval_ex(zend_write, expr, indent);
}
/* }}} */
ZEND_API int zend_print_zval_ex(zend_write_func_t write_func, zval *expr, int indent) /* {{{ */
{
zval expr_copy;
int use_copy;
zend_make_printable_zval(expr, &expr_copy, &use_copy);
if (use_copy) {
expr = &expr_copy;
}
if (Z_STRLEN_P(expr) == 0) { /* optimize away empty strings */
if (use_copy) {
zval_dtor(expr);
}
return 0;
}
write_func(Z_STRVAL_P(expr), Z_STRLEN_P(expr));
if (use_copy) {
zval_dtor(expr);
}
return Z_STRLEN_P(expr);
}
/* }}} */到这里可以看到，最终是由zend_write来执行，zend_write是一个函数指针，在zend_sartup里赋值
int zend_startup(zend_utility_functions *utility_functions, char **extensions TSRMLS_DC) /* {{{ */
{
/*......省略部分.......*/
/* Set up utility functions and values */
zend_error_cb = utility_functions->error_function;
zend_printf = utility_functions->printf_function;
zend_write = (zend_write_func_t) utility_functions->write_function;
/*.....省略部分......*/
}php_output_startup(); //这个函数注意，里面有函数指针赋值
zuf.error_function = php_error_cb;
zuf.printf_function = php_printf;
zuf.write_function = php_output_wrapper;
zuf.fopen_function = php_fopen_wrapper_for_zend;
zuf.message_handler = php_message_handler_for_zend;
zuf.block_interruptions = sapi_module.block_interruptions;
zuf.unblock_interruptions = sapi_module.unblock_interruptions;
zuf.get_configuration_directive = php_get_configuration_directive_for_zend;
zuf.ticks_function = php_run_ticks;
zuf.on_timeout = php_on_timeout;
zuf.stream_open_function = php_stream_open_for_zend;
zuf.vspprintf_function = vspprintf;
zuf.getenv_function = sapi_getenv;
zuf.resolve_path_function = php_resolve_path_for_zend;
zend_startup(&zuf, NULL TSRMLS_CC);static int php_output_wrapper(const char *str, uint str_length)
{
TSRMLS_FETCH();
return php_output_write(str, str_length TSRMLS_CC);
}
/* }}} */
PHPAPI int php_output_write(const char *str, size_t len TSRMLS_DC)
{
if (OG(flags) & PHP_OUTPUT_DISABLED) {
return 0;
}
if (OG(flags) & PHP_OUTPUT_ACTIVATED) {
php_output_op(PHP_OUTPUT_HANDLER_WRITE, str, len TSRMLS_CC);
return (int) len;
}
return php_output_direct(str, len);
}
/* }}} */php_output_direct被 php_output_startup函数赋值为php_output_stdout
PHPAPI void php_output_startup(void)
{
ZEND_INIT_MODULE_GLOBALS(output, php_output_init_globals, NULL);
zend_hash_init(&php_output_handler_aliases, 0, NULL, NULL, 1);
zend_hash_init(&php_output_handler_conflicts, 0, NULL, NULL, 1);
zend_hash_init(&php_output_handler_reverse_conflicts, 0, NULL, (void (*)(void *)) zend_hash_destroy, 1);
php_output_direct = php_output_stdout;
}
/* }}} *//* {{{ stderr/stdout writer if not PHP_OUTPUT_ACTIVATED */
static int php_output_stdout(const char *str, size_t str_len)
{
fwrite(str, 1, str_len, stdout);
return str_len;
}最终echo的结果是fwrite。
最后总结一下，var_dump函数把变量的具体信息都打印了出来，如果是数组的话，就循环输出；echo则是zend来解析的一个opcode，最终调用的是fwrite函数。
另外，echo中输出的是zval结构体中的value.str.val
Z_STRVAL_P(zval *expr)#define Z_STRVAL_P(zval_p) Z_STRVAL(*zval_p)
#define Z_STRVAL(zval) (zval).value.str.val
typedef struct _zval_struct zval;
struct _zval_struct {
/* Variable information */
zvalue_value value; /* value */
zend_uint refcount__gc;
zend_uchar type; /* active type */
zend_uchar is_ref__gc;
};
typedef union _zvalue_value {
long lval; /* long value */
double dval; /* double value */
struct {
char *val; //可以看到echo输出的这部分内容
int len;
} str;
HashTable *ht; /* hash table value */
zend_object_value obj;
zend_ast *ast;
} zvalue_value;针对echo 打印的具体内容分析，可以看到
zend_make_printable_zval(expr, &expr_copy, &use_copy); //分析这个函数ZEND_API void zend_make_printable_zval(zval *expr, zval *expr_copy, int *use_copy) /* {{{ */
{
if (Z_TYPE_P(expr)==IS_STRING) {
*use_copy = 0;
return;
}
switch (Z_TYPE_P(expr)) {
case IS_NULL:
Z_STRLEN_P(expr_copy) = 0;
Z_STRVAL_P(expr_copy) = STR_EMPTY_ALLOC();
break;
case IS_BOOL:
if (Z_LVAL_P(expr)) {
Z_STRLEN_P(expr_copy) = 1;
Z_STRVAL_P(expr_copy) = estrndup("1", 1);
} else {
Z_STRLEN_P(expr_copy) = 0;
Z_STRVAL_P(expr_copy) = STR_EMPTY_ALLOC();
}
break;
case IS_RESOURCE:
Z_STRVAL_P(expr_copy) = (char *) emalloc(sizeof("Resource id #") - 1 + MAX_LENGTH_OF_LONG);
Z_STRLEN_P(expr_copy) = snprintf(Z_STRVAL_P(expr_copy), sizeof("Resource id #") - 1 + MAX_LENGTH_OF_LONG, "Resource id #%ld", Z_LVAL_P(expr));
break;
case IS_ARRAY:
zend_error(E_NOTICE, "Array to string conversion");
Z_STRLEN_P(expr_copy) = sizeof("Array") - 1;
Z_STRVAL_P(expr_copy) = estrndup("Array", Z_STRLEN_P(expr_copy));
break;
case IS_OBJECT:
{
TSRMLS_FETCH();
if (zend_std_cast_object_tostring(expr, expr_copy, IS_STRING TSRMLS_CC) == SUCCESS) {
break;
}
if (Z_OBJ_HANDLER_P(expr, cast_object)) {
zval *val;
ALLOC_ZVAL(val);
INIT_PZVAL_COPY(val, expr);
zval_copy_ctor(val);
if (Z_OBJ_HANDLER_P(expr, cast_object)(val, expr_copy, IS_STRING TSRMLS_CC) == SUCCESS) {
zval_ptr_dtor(&val);
break;
}
zval_ptr_dtor(&val);
}
if (!Z_OBJ_HANDLER_P(expr, cast_object) && Z_OBJ_HANDLER_P(expr, get)) {
zval *z = Z_OBJ_HANDLER_P(expr, get)(expr TSRMLS_CC);
Z_ADDREF_P(z);
if (Z_TYPE_P(z) != IS_OBJECT) {
zend_make_printable_zval(z, expr_copy, use_copy);
if (*use_copy) {
zval_ptr_dtor(&z);
} else {
ZVAL_ZVAL(expr_copy, z, 0, 1);
*use_copy = 1;
}
return;
}
zval_ptr_dtor(&z);
}
zend_error(EG(exception) ? E_ERROR : E_RECOVERABLE_ERROR, "Object of class %s could not be converted to string", Z_OBJCE_P(expr)->name);
Z_STRLEN_P(expr_copy) = 0;
Z_STRVAL_P(expr_copy) = STR_EMPTY_ALLOC();
}
break;
case IS_DOUBLE:
*expr_copy = *expr;
zval_copy_ctor(expr_copy);
zend_locale_sprintf_double(expr_copy ZEND_FILE_LINE_CC);
break;
default:
*expr_copy = *expr;
zval_copy_ctor(expr_copy);
convert_to_string(expr_copy);
break;
}
Z_TYPE_P(expr_copy) = IS_STRING;
*use_copy = 1;
}
/* }}} */其他的类型确实很好解决，object的话，需要先找找tostring函数，然后再查找object的两个句柄函数cast_object和get
继续挖掘object的cast_object和get发现
ZEND_API zend_object_handlers std_object_handlers = {
zend_objects_store_add_ref, /* add_ref */
zend_objects_store_del_ref, /* del_ref */
zend_objects_clone_obj, /* clone_obj */
zend_std_read_property, /* read_property */
zend_std_write_property, /* write_property */
zend_std_read_dimension, /* read_dimension */
zend_std_write_dimension, /* write_dimension */
zend_std_get_property_ptr_ptr, /* get_property_ptr_ptr */
NULL, /* get */
NULL, /* set */
zend_std_has_property, /* has_property */
zend_std_unset_property, /* unset_property */
zend_std_has_dimension, /* has_dimension */
zend_std_unset_dimension, /* unset_dimension */
zend_std_get_properties, /* get_properties */
zend_std_get_method, /* get_method */
NULL, /* call_method */
zend_std_get_constructor, /* get_constructor */
zend_std_object_get_class, /* get_class_entry */
zend_std_object_get_class_name, /* get_class_name */
zend_std_compare_objects, /* compare_objects */
zend_std_cast_object_tostring, /* cast_object */
NULL, /* count_elements */
zend_std_get_debug_info, /* get_debug_info */
zend_std_get_closure, /* get_closure */
zend_std_get_gc, /* get_gc */
NULL, /* do_operation */
NULL, /* compare */
};水平有限，文中有错误之处还望各位指正！
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