字符串函数学习一

1.wordwrap 打断字符串为指定数量的字串

$text="shang ban jiu shi wei le huo zhe ";
$new_text=wordwrap($text,20,"<br/>\n");
print_r($new_text);

2.vsprintf 返回格式化字符串

print_r(vsprintf("%04d-%02d-%02d",explode('-','2020-10-1')));

3.vprintf 输出格式化字符串

print_r(vprintf("%04d-%02d-%02d",explode('-','2020-10-1')));

4. ucwords将字符串中每个单词的首字母转换为大写

$text1='come on';
echo(ucwords($text1)).("<br/>\n");


$text2='COME ON';
echo(strtolower($text2)).("<br/>\n");
echo(ucwords(strtolower($text2))).("<br/>\n");

$text3='come|on';
echo(ucwords($text3)).("<br/>\n");
echo(ucwords($text3,'|')).("<br/>\n");

5.ucfirst 将字符串的首字母转换为大写

$text1='come on';
echo(ucfirst($text1)).("<br/>\n");


$text2='COME ON';
echo(strtolower($text2)).("<br/>\n");
echo(ucfirst(strtolower($text2))).("<br/>\n");

$text3='come|on';
echo(ucfirst($text3)).("<br/>\n");

6.trim 去除字符串收尾处的空白字符（或其他字符）

$text1=' come on ';
echo(trim($text1)).("<br/>\n");


$text2='CCOME ONC';
echo(trim($text2,'C')).("<br/>\n");

$text3='come on|';
echo(trim($text3,'|')).("<br/>\n");

7.substr 返回字符串的子串

$rest = substr("abcdef", 1); //返回"bcdef"
$rest = substr("abcdef", 1,4); //返回"bcde"
$rest = substr("abcdef", 0, -1);  // 返回 "abcde"
$rest = substr("abcdef", 2, -1);  // 返回 "cde"
$rest = substr("abcdef", 4, -4);  // 返回 ""
$rest = substr("abcdef", -3, -1); // 返回 "de"

8.substr_replace替换字符串的子串

echo substr_replace("Hello","world",0);

echo substr_replace("Hello world","Shanghai",6);

echo substr_replace("Hello world","Shanghai",-5);

echo substr_replace("world","Hello ",0,0);

$replace = array("1: AAA","2: AAA","3: AAA");
echo implode("<br>",substr_replace($replace,'BBB',3,3));

9.substr_count()计算字串出现的次数

$text = 'This is a test';
echo strlen($text); //14

echo substr_count($text, 'is'); //2

// 字符串被简化为 's is a test'，因此输出 1
echo substr_count($text, 'is', 3);

// 字符串被简化为 's i'，所以输出 0
echo substr_count($text, 'is', 3, 3);

// 因为 5+10 > 14，所以生成警告
echo substr_count($text, 'is', 5, 10);

// 输出 1，因为该函数不计算重叠字符串
$text2 = 'gcdgcdgcd';
echo substr_count($text2, 'gcdgcd');

10.substr_compare 二进制安全比较字符串(从偏移位置比较指定长度）

echo substr_compare("abcde", "bc", 1, 2); // 0
echo substr_compare("abcde", "de", -2, 2); // 0
echo substr_compare("abcde", "bcg", 1, 2); // 0
echo substr_compare("abcde", "BC", 1, 2, true); // 0
echo substr_compare("abcde", "bc", 1, 3); // 1
echo substr_compare("abcde", "cd", 1, 2); // -1
echo substr_compare("abcde", "abc", 5, 1); // warning

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