PHP 字符串
Single vs double quotes, common string functions, and multibyte handling.
Key PointsDouble quotes interpolate variables and escapes; single quotes are almost literal.
单引号与双引号
The most basic difference: **single quotes only escape \' and \\**; double quotes interpolate variables and sequences like \n, \t, \$.
PHP
<?php
$name = "Tom";
echo 'Hello $name\n'; // 原样输出
echo "Hello $name\n"; // 解析变量
echo 'C:\path\to'; // \p \t 在单引号里不转义
echo "\n";
echo "价格: {$name}100\n"; // 用 {} 明确边界
echo "价格: $name" . "100\n"; // 或直接拼接Output
Hello $name\nHello Tom
C:\path\to
价格: Tom100
价格: Tom100The first line runs together because
\n inside single quotes does not create a newline. That is the practical dividing line between the two quote styles.Single quotes are marginally faster, but the difference is negligible. Follow the team convention.
常用函数
PHP
<?php
$s = " Hello PHP ";
echo strlen($s), "\n"; // 含空格
echo strlen(trim($s)), "\n"; // 去首尾空白
echo strtoupper($s), "\n";
echo ucfirst("hello"), "\n";
echo strpos("hello php", "php"), "\n"; // 位置从 0 开始
echo substr("hello php", 6), "\n";
echo substr("hello php", -3), "\n";
echo str_replace("php", "PHP", "hello php"), "\n";
echo str_repeat("ab", 3), "\n";
echo str_pad("7", 3, "0", STR_PAD_LEFT), "\n";
echo implode("-", [1, 2, 3]), "\n";
echo sprintf("%05.2f", 3.14159), "\n";
echo number_format(1234567.891, 2), "\n";Output
13
9
HELLO PHP
Hello
6
php
php
hello PHP
ababab
007
1-2-3
03.14
1,234,567.89拆分与合并
PHP
<?php
$csv = "apple,banana,cherry";
$arr = explode(",", $csv);
print_r($arr);
echo implode(" | ", $arr), "\n";
echo count($arr), "\n";
// 限制拆分段数
print_r(explode(",", $csv, 2));
// str_split 按长度切
print_r(str_split("abcdef", 2));Output
Array
(
[0] => apple
[1] => banana
[2] => cherry
)
apple | banana | cherry
3
Array
(
[0] => apple
[1] => banana,cherry
)
Array
(
[0] => ab
[1] => cd
[2] => ef
)多字节字符串
strlen counts bytes; a UTF-8 Chinese character is 3 bytes. Use the mb_* family to count characters.
PHP
<?php
$cn = "你好世界";
echo strlen($cn), "\n"; // 字节数
echo mb_strlen($cn), "\n"; // 字符数
echo mb_substr($cn, 1, 2), "\n"; // 从第 2 个字取 2 个
echo mb_strtoupper("straße"), "\n";Output
12
4
好世
STRASSEsubstr() can slice a Chinese character in half and produce garbage. For any CJK text use mb_substr, mb_strlen, mb_strpos.格式化输出
| Specifier | Meaning | Example |
|---|---|---|
| %s | 字符串 | sprintf("%s", "a") → a |
| %d | 十进制整数 | sprintf("%d", 3.9) → 3 |
| %f | 浮点（默认 6 位小数） | sprintf("%f", 1.5) → 1.500000 |
| %.2f | 保留 2 位小数 | sprintf("%.2f", 1.005) → 1.00 |
| %05d | 补零到 5 位 | sprintf("%05d", 42) → 00042 |
| %x | 十六进制小写 | sprintf("%x", 255) → ff |
| %b | 二进制 | sprintf("%b", 5) → 101 |
| %% | 百分号本身 | sprintf("%%") → % |
sprintf returns the string, printf prints it. For numbers with units sprintf reads better than manual concatenation.
单引号与双引号
这是 PHP 里最基础也最容易踩的差异：**单引号只有 \' 和 \\ 两个转义**，其余一律原样；双引号会解析变量、\n、\t、\$ 等。
PHP
<?php
$name = "Tom";
echo 'Hello $name\n'; // 原样输出
echo "Hello $name\n"; // 解析变量
echo 'C:\path\to'; // \p \t 在单引号里不转义
echo "\n";
echo "价格: {$name}100\n"; // 用 {} 明确边界
echo "价格: $name" . "100\n"; // 或直接拼接Output
Hello $name\nHello Tom
C:\path\to
价格: Tom100
价格: Tom100第一条输出是
Hello $name\nHello Tom 连在一起——单引号里的 \n 没有换行效果。这正是「该用双引号还是单引号」的分水岭：要换行就得用双引号。性能上单引号略快（不用扫描变量），但差异小到可以忽略。团队规范统一即可，不必为此纠结。
常用函数
PHP
<?php
$s = " Hello PHP ";
echo strlen($s), "\n"; // 含空格
echo strlen(trim($s)), "\n"; // 去首尾空白
echo strtoupper($s), "\n";
echo ucfirst("hello"), "\n";
echo strpos("hello php", "php"), "\n"; // 位置从 0 开始
echo substr("hello php", 6), "\n";
echo substr("hello php", -3), "\n";
echo str_replace("php", "PHP", "hello php"), "\n";
echo str_repeat("ab", 3), "\n";
echo str_pad("7", 3, "0", STR_PAD_LEFT), "\n";
echo implode("-", [1, 2, 3]), "\n";
echo sprintf("%05.2f", 3.14159), "\n";
echo number_format(1234567.891, 2), "\n";Output
13
9
HELLO PHP
Hello
6
php
php
hello PHP
ababab
007
1-2-3
03.14
1,234,567.89拆分与合并
PHP
<?php
$csv = "apple,banana,cherry";
$arr = explode(",", $csv);
print_r($arr);
echo implode(" | ", $arr), "\n";
echo count($arr), "\n";
// 限制拆分段数
print_r(explode(",", $csv, 2));
// str_split 按长度切
print_r(str_split("abcdef", 2));Output
Array
(
[0] => apple
[1] => banana
[2] => cherry
)
apple | banana | cherry
3
Array
(
[0] => apple
[1] => banana,cherry
)
Array
(
[0] => ab
[1] => cd
[2] => ef
)多字节字符串
strlen 数的是字节，中文 UTF-8 一个字 3 字节。要按「字」数必须用 mb_* 系列。
PHP
<?php
$cn = "你好世界";
echo strlen($cn), "\n"; // 字节数
echo mb_strlen($cn), "\n"; // 字符数
echo mb_substr($cn, 1, 2), "\n"; // 从第 2 个字取 2 个
echo mb_strtoupper("straße"), "\n";Output
12
4
好世
STRASSEsubstr() 切中文很可能把半个字符切出来，得到乱码。项目里只要涉及中文，一律用 mb_substr / mb_strlen / mb_strpos。格式化输出
| 占位符 | 含义 | 示例 |
|---|---|---|
| %s | 字符串 | sprintf("%s", "a") → a |
| %d | 十进制整数 | sprintf("%d", 3.9) → 3 |
| %f | 浮点（默认 6 位小数） | sprintf("%f", 1.5) → 1.500000 |
| %.2f | 保留 2 位小数 | sprintf("%.2f", 1.005) → 1.00 |
| %05d | 补零到 5 位 | sprintf("%05d", 42) → 00042 |
| %x | 十六进制小写 | sprintf("%x", 255) → ff |
| %b | 二进制 | sprintf("%b", 5) → 101 |
| %% | 百分号本身 | sprintf("%%") → % |
sprintf 返回格式化后的字符串，printf 直接输出。拼接数字和单位时用 sprintf 比手写 . 更清楚。