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PHP学习之输出字符串(echo,print,printf,print_r和var_dump)_php基础

May 17, 2016 am 09:01 AM
echo print printf var_dump

下面一一进行介绍。
1. echo
echo 是PHP的一个关键字,它没有返回值。在写法上,它可以省略小括号。如下代码:

复制代码 代码如下:

echo 'Test String';
echo('Test String');

2. print
print 也是PHP的一个关键字,它有返回值,一般返回true,返回false的情况应该没有。在写法上,它和echo一样,可以省略小括号。如下代码:
复制代码 代码如下:

print 'Test String';
print('Test String');

3. printf
printf可以像C语言的printf一样,格式化输出一个字符串。它的格式和C语言差不多,都是以%开头。其说明符定义如下。
b 参数为整数,显示其二进制
c 参数为整数,显示对应ASCII字符
d 参数为整数,显示其十进制
f 参数为双精度,显示为浮点数
e 参数为双精度,显示为科学计数型
g 参数为双精度,显示为浮点数或科学计数型
o 参数为整数,显示其八进制
s 参数为字符串,显示为字符串
u 参数为无符号整数,显示其十进制
x/X 参数为整数,显示其十六进制(分别为大小写显示)
% 输出%要说明的是:
f,e默认小数点后六位,g在超过六位(加小数点)时,会四舍五入,如果四舍五入之后的值小于1000000会直接输出,大于的1000000的话会显示成科学计数型。f在值大于1.2e23输出的结果是不对的。
以上除%以外,其它的都可以指定输出总位数(小数点、E都算一位),并可以指定0或空格为补位符,还可以指定补位在左还是在右。
f,e可以指定小数点后位数。
如 %5d 表示输出总位数为5,不足左补空格; %05d 表示输出总位数为5,不足左补0; %05.1f 表示输出总位数为5,不足左补0,小数点后1位; %-05.1f 表示输出总位数为5,不足右补0,小数点后1位;
示例代码:
复制代码 代码如下:

printf("%7.2f", 1.2); // " 1.20"
printf("%-07.2f", 1.2); // "1.20000"

4. sprintf
sprintf和格式转换和printf一样,两者区别在于printf直接输出,而sprintf返回一个格式化后的字符串。
5. print_r和var_dump
print_r和var_dump都能输出数组和对象,但print_r对布尔型的输出不太明显;var_dump输出比较详细,一般调试时用得多。
如下代码:
复制代码 代码如下:

$v = new test();
print_r($v);
var_dump($v);
class test {
public $num = 1;
public $str = "222";
public $bln = true;

结果为:
复制代码 代码如下:

test Object
(
[num] => 1
[str] => 222
[bool] => 1
)
object(test)#1 (3) {
["num"]=>
int(1)
["str"]=>
string(3) "222"
["bool"]=>
bool(true)
}

参考资料:
PHP程序设计,2003,第四章 字符串,输出字符串
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