PHP中各种数据类型的区别和转换方法

<?php$a = 7;$b = 'abcdsfdf';echo $a . $b;?>

if (UNEXPECTED(Z_TYPE_P(op1) != IS_STRING)) {if (Z_ISREF_P(op1)) {   op1 = Z_REFVAL_P(op1);if (Z_TYPE_P(op1) == IS_STRING) break;}ZEND_TRY_BINARY_OBJECT_OPERATION(ZEND_CONCAT, concat_function);use_copy1 = zend_make_printable_zval(op1, &op1_copy);

<?php$double = 5.2323;echo (int)$double;?>

PHP_FUNCTION(settype){    zval *var;    char *type;    size_t type_len = 0;    if (zend_parse_parameters(ZEND_NUM_ARGS(), "zs", &var, &type, &type_len) == FAILURE) {        return;    }    ZVAL_DEREF(var);    if (!strcasecmp(type, "integer")) {        convert_to_long(var);    } else if (!strcasecmp(type, "int")) {        convert_to_long(var);    } else if (!strcasecmp(type, "float")) {        convert_to_double(var);    } else if (!strcasecmp(type, "double")) { /* deprecated */        convert_to_double(var);    } else if (!strcasecmp(type, "string")) {        convert_to_string(var);    } else if (!strcasecmp(type, "array")) {        convert_to_array(var);    } else if (!strcasecmp(type, "object")) {        convert_to_object(var);    } else if (!strcasecmp(type, "bool")) {        convert_to_boolean(var);    } else if (!strcasecmp(type, "boolean")) {        convert_to_boolean(var);    } else if (!strcasecmp(type, "null")) {        convert_to_null(var);    } else if (!strcasecmp(type, "resource")) {        php_error_docref(NULL, E_WARNING, "Cannot convert to resource type");        RETURN_FALSE;    } else {        php_error_docref(NULL, E_WARNING, "Invalid type");        RETURN_FALSE;    }    RETVAL_TRUE;}