scanf() 函数可以获取到终端字符串，但是不能识别到空格字符，遇到空格会终止，空格后面的字符串会在缓冲区中，下次获取时会继续用。
gets()函数以回车字符进行标识，获取用户输入字符串以回车为终止符。
scanf和gets函数都是不安全的，如果目标字符串缓冲区无法存储我们输入的字符串，会导致段错误
fgets()函数限定了获取字符串的长度，如果输入字符串过多，依然可以只获取限定长度的字符串，剩下的字符串还在输入缓冲区中。
测试demo以及输入测试描述： #include <stdio.h>#include <stdlib.h>#include <string.h>//scanf输入遇到空格会当成结束符//gets是遇到回车结束 fgets其实对gets的一些完善扩展int main(){//scanf 读取终端内容时 遇到空格会终止// 终止后剩余的结果其实还在终端缓冲区中，会在后面读取缓冲区继续生效char data[20];printf("please test of scanf :n");scanf("%s", data);printf("scanf func get data is [%s] n", data);memset(data, 0, 20);printf("please test of space scanf :n");scanf("%s", data);printf("scanf func get data is [%s] n", data);memset(data, 0, 20);fflush(stdin);//可以刷新缓冲区 一般用在读数据后没读完//gets可以读取换行前的所有字符，但是gets是不安全的，如无法保证长度越界printf("please test of gets n");gets(data);printf("gets func get data is [%s] n", data);memset(data, 0, 20);printf("please test of space gets :n");gets(data);printf("gets func get data is [%s] n", data);memset(data, 0, 20);//使用fgets函数 对gets函数的扩展，限定了读取数据的长度printf("plese test of fgets : n");fgets(data, 20, stdin); //字符串地址 字符串长度 读入的文件 printf("fgets func get data is : [%s]", data);memset(data, 0, 20);printf("please test of len out of 20 fgets:n");fgets(data, 20, stdin);printf("fgets func get data is : [%s] n", data);memset(data, 0, 20);fflush(stdin);return 0;}/********************************************输出的结果：hlp@ubuntu:~/com_port$ ./inplease test of scanf : ==>scanf正常输入12334scanf func get data is [12334] ==》打印获取终端的输入please test of space scanf :==》scanf输入带空格的字符串123 1231 scanf func get data is [123] ==》发现只打印了空格前的字符串please test of gets gets func get data is [ 1231 ] ==》没有经过手动输入， get函数直接获取到终端缓冲区中已经存在的字符串please test of space gets :==》get函数测试带空格的字符串123 123 412gets func get data is [123 123 412] ==》get函数能打印带空格的字符串，终结符以回车为准plese test of fgets : ==》测试fget函数获取，在长度内，发现获取到终端内的回车字符123123 123 1fgets func get data is : [123123 123 1]please test of len out of 20 fgets:==》如果超过fgets函数参数限制的长度，获取到输入的固定长度字符19个字符12312 1231231 12312 123123 12312123fgets func get data is : [12312 1231231 12312]**************************************************//********************************************可以看出，输入字符串过长，scanf和get函数如果获取长度过多，都会引发段错误hlp@ubuntu:~/com_port$ ./inplease test of scanf :1scanf func get data is [1] please test of space scanf :1scanf func get data is [1] please test of gets gets func get data is [] please test of space gets :111111111111111111111111111111111111111111gets func get data is [111111111111111111111111111111111111111111] plese test of fgets : 12fgets func get data is : [12]please test of len out of 20 fgets:12fgets func get data is : [12*** stack smashing detected ***: <unknown> terminatedAborted (core dumped)hlp@ubuntu:~/com_port$ ./inplease test of scanf :111111111111111111111111111111111111111scanf func get data is [111111111111111111111111111111111111111] please test of space scanf :11111111111111111111111111111111111scanf func get data is [11111111111111111111111111111111111] please test of gets gets func get data is [] please test of space gets :1gets func get data is [1] plese test of fgets : 1fgets func get data is : [1]please test of len out of 20 fgets:1fgets func get data is : [1*** stack smashing detected ***: <unknown> terminatedAborted (core dumped)**************************************************//********************************************可以看出，输入字符串过长，如果用fget函数进行获取，会在限制长度内获取，下次继续获取缓冲区中剩余字段hlp@ubuntu:~/com_port$ ./inplease test of scanf :1scanf func get data is [1] please test of space scanf :1scanf func get data is [1] please test of gets gets func get data is [] please test of space gets :1gets func get data is [1] plese test of fgets : 1111111111111111111111111111111111111111111111111111111111111111111111111fgets func get data is : [1111111111111111111]please test of len out of 20 fgets:fgets func get data is : [1111111111111111111]**************************************************/