Linux 读取stdio.h文件

我已经用gcc在linux下编译了我的C程序，并保存了所有的临时文件。在.i文件中，stdio.h文件已展开。我一直在试着读它，但我不理解开头几行的意思

# 1 "<built-in>"
# 1 "<command-line>"
# 1 "app.c"
# 1 "/usr/include/stdio.h" 1 3 4
# 28 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/features.h" 1 3 4
# 313 "/usr/include/features.h" 3 4
# 1 "/usr/include/bits/predefs.h" 1 3 4
# 314 "/usr/include/features.h" 2 3 4
# 346 "/usr/include/features.h" 3 4
# 1 "/usr/include/sys/cdefs.h" 1 3 4
# 353 "/usr/include/sys/cdefs.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 354 "/usr/include/sys/cdefs.h" 2 3 4
# 347 "/usr/include/features.h" 2 3 4

#1“
# 1 ""
#1“附录c”
#1“/usr/include/stdio.h”1 3 4
#28“/usr/include/stdio.h”3 4
#1“/usr/include/features.h”1 3 4
#313“/usr/include/features.h”3 4
#1“/usr/include/bits/predefs.h”1 3 4
#314“/usr/include/features.h”2 3 4
#346“/usr/include/features.h”3 4
#1“/usr/include/sys/cdefs.h”1 3 4
#353“/usr/include/sys/cdefs.h”3 4
#1“/usr/include/bits/wordsize.h”1 3 4
#354“/usr/include/sys/cdefs.h”2 3 4
#347“/usr/include/features.h”2 3 4

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我认为#符号后面的数字是行号，但每行末尾1,2,3,4的意义是什么？提前感谢：）

哦，很抱歉我找到了，这些是标志1-新文件的开始2-返回到以前的文件3-以下文本来自系统头文件（#include vs#include“”）4-以下文本应被视为包装在隐式外部“C”块中。您应该添加它作为答案，然后！