PHP基础温习之echo print printf sprintf print_r var_dump的用法与区别
一、echo
echo() 实际上不是一个函数,是php语句,因此您无需对其使用括号。不过,如果您希望向 echo() 传递一个以上的参数,那么使用括号会发生解析错误。而且echo是返回void的,并不返回值,所以不能使用它来赋值。
例子:
复制代码代码如下:
<span style="color: #000000;">php </span><span style="color: #800080;">$a</span> = <span style="color: #0000ff;">echo</span>("55nav"); <span style="color: #008000;">//</span><span style="color: #008000;"> 错误!不能用来赋值 </span><span style="color: #0000ff;">echo</span> "55nav"; <span style="color: #008000;">//</span><span style="color: #008000;"> 55nav </span><span style="color: #0000ff;">echo</span> ("55nav"); <span style="color: #008000;">//</span><span style="color: #008000;"> 55nav </span><span style="color: #0000ff;">echo</span> ("55nav","com"); <span style="color: #008000;">//</span><span style="color: #008000;">发生错误,有括号不能传递多个参数 </span><span style="color: #0000ff;">echo</span> "55nav"," com"," is", " web"; <span style="color: #008000;">//</span><span style="color: #008000;"> 不用括号的时候可以用逗号隔开多个值, 会输出 55nav com is web </span><span style="color: #0000ff;">echo</span> "55nav is 8 good 9 web."; <span style="color: #008000;">//</span><span style="color: #008000;"> 不管是否换行,最终显示都是为一行 55nav is good web. </span><span style="color: #800080;">$fistname</span>="55nav"<span style="color: #000000;">; </span><span style="color: #0000ff;">echo</span> "<span style="color: #800080;">$fistname</span> com"; <span style="color: #008000;">//</span><span style="color: #008000;"> 如果 $firstname = "55nav", 则会输出 55nav com. </span><span style="color: #0000ff;">echo</span> '$firstname com'; <span style="color: #008000;">//</span><span style="color: #008000;"> 由于使用单引号,所以不会输出$firstname的值,而是输出 $firstname com </span>?>
二、print
print() 和 echo() 用法一样,但是echo速度会比print快一点点。实际上它也不是一个函数,因此您无需对其使用括号。不过,如果您希望向print() 传递一个以上的参数,那么使用括号会发生解析错误。注意print总是返回1的,这个和echo不一样,也就是可以使用print来赋值,不过没有实际意义。
例子:
复制代码代码如下:
<span style="color: #000000;">php </span><span style="color: #800080;">$a</span> = <span style="color: #0000ff;">print</span>("55nav"); <span style="color: #008000;">//</span><span style="color: #008000;"> 这个是允许的 </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$a</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> $a的值是1 </span>?>
三、print_r 函数
print_r函数打印关于变量的易于理解的信息。
语法:mixed print_r ( mixed $expression [, bool return ] )
如果变量是string , integer or float , 将会直接输出其值,如果变量是一个数组,则会输出一个格式化后的数组,便于阅读,也就是有key和value对应的那种格式。对于object对象类同。print_r有两个参数,第一个是变量,第二个可设为true,如果设为true,则会返回字符串,否则返回布尔值TRUE。
例子:
复制代码代码如下:
<span style="color: #000000;">php </span><span style="color: #800080;">$a</span>="55nav"<span style="color: #000000;">; </span><span style="color: #800080;">$c</span> = <span style="color: #008080;">print_r</span>(<span style="color: #800080;">$a</span><span style="color: #000000;">); </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$c</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> $c的值是TRUE </span> <span style="color: #800080;">$c</span> = <span style="color: #008080;">print_r</span>(<span style="color: #800080;">$a</span>,<span style="color: #0000ff;">true</span><span style="color: #000000;">); </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$c</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> $c的值是字符串55nav </span> ?>
四、printf函数
printf函数返回一个格式化后的字符串。
语法:printf(format,arg1,arg2,arg++)
参数 format 是转换的格式,以百分比符号 (“%”) 开始到转换字符结束。下面是可能的 format 值:
* %% – 返回百分比符号
* %b – 二进制数
* %c – 依照 ASCII 值的字符
* %d – 带符号十进制数
* %e – 可续计数法(比如 1.5e+3)
* %u – 无符号十进制数
* %f – 浮点数(local settings aware)
* %F – 浮点数(not local settings aware)
* %o – 八进制数
* %s – 字符串
* %x – 十六进制数(小写字母)
* %X – 十六进制数(大写字母)
arg1, arg2, arg++ 等参数将插入到主字符串中的百分号 (%) 符号处。该函数是逐步执行的,在第一个 % 符号中,插入 arg1,在第二个 % 符号处,插入 arg2,依此类推。如果 % 符号多于 arg 参数,则您必须使用占位符。占位符被插入 % 符号之后,由数字和 “\$” 组成。可使用数字指定显示的参数,详情请看例子。
例子:
复制代码代码如下:
<span style="color: #000000;">php </span><span style="color: #008080;">printf</span>("My name is %s %s。","55nav", "com"); <span style="color: #008000;">//</span><span style="color: #008000;"> My name is 55nav com。 </span><span style="color: #008080;">printf</span>("My name is %1\$s %1\$s","55nav", "com"); <span style="color: #008000;">//</span><span style="color: #008000;"> 在s前添加1\$或2\$.....表示后面的参数显示的位置,此行输出 My name is 55nav 55nav因为只显示第一个参数两次。 </span><span style="color: #008080;">printf</span>("My name is %2\$s %1\$s","55nav", "com"); <span style="color: #008000;">//</span><span style="color: #008000;"> My name is com 55nav </span>?>
五、sprintf函数
此函数使用方法和printf一样,唯一不同的就是该函数把格式化的字符串写写入一个变量中,而不是输出来。
例子:
复制代码代码如下:
<span style="color: #000000;">php </span><span style="color: #008080;">sprintf</span>("My name is %1\$s %1\$s","55nav", "com"); <span style="color: #008000;">//</span><span style="color: #008000;">你会发现没有任何东西输出的。 </span><span style="color: #800080;">$out</span> = <span style="color: #008080;">sprintf</span>("My name is %1\$s %2\$s","55nav", "com"<span style="color: #000000;">); </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$out</span>; <span style="color: #008000;">//</span><span style="color: #008000;">输出 My name is 55nav com </span>?>
六、var_dump函数
功能: 输出变量的内容、类型或字符串的内容、类型、长度。常用来调试。
复制代码代码如下:
<span style="color: #000000;">php </span><span style="color: #800080;">$a</span>=100<span style="color: #000000;">; </span><span style="color: #008080;">var_dump</span>(<span style="color: #800080;">$a</span>); <span style="color: #008000;">//</span><span style="color: #008000;">int(100) </span><span style="color: #800080;">$a</span>=100.356<span style="color: #000000;">; </span><span style="color: #008080;">var_dump</span>(<span style="color: #800080;">$a</span>); <span style="color: #008000;">//</span><span style="color: #008000;">float(100.356) </span>?>

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