This function should be called after you initialize a CURL session and all the options for the session are set. Its purpose is simply to execute the predefined CURL session (given by the ch).
提示: 为了防止程序直接将结果输出到浏览器,您可以使用输出控制函数(output-control functions)来捕获函数的输出,并把它们保存到一个 string 型的变量中。