今天玩耍的是include conflicts
如果你include多个header文件，要保证里面没有冲突的定义。
比如这样：
header1.h

typedef char yes_t[6];

header2.h

typedef char yes_t[7];

main.c

#include <header1.h>
#include <header2.h>
#include <stdio.h>

int main(int argc, char **argv) {
    yes_t a = "Yes!";
    puts(a);
    return 0;
}

gcc -o test -I. test.c

In file included from test.c:2:0:
./header2.h:1:14: error: conflicting types for ‘yes_t’
 typedef char yes_t[7];
              ^~~~~
In file included from test.c:1:0:
./header1.h:1:14: note: previous declaration of ‘yes_t’ was here
 typedef char yes_t[6];
              ^~~~~

但是如果都是yes_t[6];，那就没事了。