php如何利用函数过滤字符串的空格

//示例
str_replace($searchString, $replaceString, $originalString, $count);

//代码执行
$searchString = " ";
$replaceString = "";
$originalString = "This is a programming tutorial"; 

$outputString = str_replace($searchString, $replaceString, $originalString); 
echo "原字符串：".$originalString."
";  
echo "去除空格后的字符串：".$outputString; 

//示例
trim(string,charlist)

//代码执行
$str = "  Hello PHP中文网   ";
$newStr = trim($str); 
echo "原字符串:".$str."。
";  
echo "去除空格后的字符串:".$newStr."。
"; 

//示例
preg_replace($regexPattern, $replacementVar, $original, $limit, $count)

//代码执行
$originalString = "This is a programming tutorial"; 
$outputString = preg_replace('/\s+/', '', $originalString); 
echo "原字符串：".$originalString."
";  
echo "去除空格后的字符串：".$outputString."
"; 

//利用$limit限制代码执行次数
$searchString = " ";
$replaceString = "";
$limit = 2;
$originalString = "This is a programming tutorial"; 
$outputString = preg_replace('/\s+/', '', $originalString,$limit); 
echo "原字符串：".$originalString."
";  
echo "去除空格后的字符串：".$outputString."
";