apcu_add('apcu_stock_1',?100);var_dump(apcu_fetch('apcu_stock_1'));?//?result:?int?0
apcu_add('apcu_stock_2',?100);var_dump(apcu_fetch('apcu_stock_2'));?//?result:?string?'100'
apcu_add('apcu_stock_3',?100);var_dump(apcu_fetch('apcu_stock_3'));?//?result:?int?100

APCu對以【apcu_stock_】開頭的變量無法正常apcu_add是什么原因？

APCu版本：php_apcu-5.1.8-7.1-ts-vc14-x64