php字符串函数不起作用

I am trying to use string function but these functions are not working in my program.

I am using following function.

echo strpos("set","namesetname");
echo strstr("set","namesetname");
echo stristr("set","namesetname");
echo strchr("set","namesetname");

all these functions are not displaying any things, nothing is returns or displayed on screen.

You used wrong syntax. Change params places reverse

echo strpos("namesetname", "set");
echo strstr("namesetname", "set");
echo stristr("namesetname", "set");
echo strchr("namesetname", "set");

strpos returns BOOLEAN or position.

Using the functions as below will solve your issue..

echo strpos("namesetname","set");
echo strstr("namesetname","set");
echo stristr("namesetname","set");
echo strchr("namesetname","set");

Below are the some links for your reference