编译为 C99 时未定义 CRTSCTS [英] CRTSCTS not define when compiling as C99
问题描述
我正在树莓派上编写一些串行代码并切换到 C99.当我这样做时,我开始收到错误消息错误:‘CRTSCTS’未声明(首次在此函数中使用)"
I'm writing some serial code on a raspberry pi and switched to C99. When I did I started getting the error "error: ‘CRTSCTS’ undeclared (first use in this function)"
$ c99 -M serial01.c | grep termios.h
/usr/include/termios.h /usr/include/arm-linux-gnueabihf/bits/termios.h
$ gcc -M serial01.c | grep termios.h
/usr/include/termios.h /usr/include/arm-linux-gnueabihf/bits/termios.h
使用 -M 会显示 2 个 termios.h 标头.前者不包含 CRTSCTS 的定义,后者包含.
using -M reveals 2 termios.h headers. the former does not contain a definition for CRTSCTS and the latter does.
我假设标准 c89 使用的是好的,而 c99 没有,但我不确定,因为 -M 调用的结果是相同的.谁能向我解释为什么在我切换到 C99 时会发生这种情况以及如何修复它?
I assume the standard c89 is using the good one and c99 not but I'm not sure since the result of the -M call is identical. Can anyone explain to me why this is happening when I switch to C99 and how to fix it?
推荐答案
-std=gnu99
是解决方案.详情如下.
-std=gnu99
is the solution. More detailed below.
gcc/c99 -M 调用的结果是相同的,但没有任何意义!这种行为的解释是预处理器宏(特别是 GNU 扩展,如 Mat 所说).
Result of the gcc/c99 -M call is identical but it does not mean anything! The explanation of this behavior are preprocessor macros (specifically GNU extensions, like said Mat).
详细说明:
cat -n main.c
1 #include <termios.h>
2
3 int printf(const char *, ...);
4
5 int main(void)
6 {
7 printf("%d
", CRTSCTS);
8 return 0;
9 }
gcc main.c -o main --std=c89 -> 'CRTSCTS' undeclared compilation error
gcc main.c -o main --std=cgnu89 -> successfully compiled
这个行为对于 c99 和 gnu99 是一样的!
This behavior is the same for c99 and gnu99!
就像 Cameron 所说的,-M 输出是相同的:
Like said Cameron, -M output is identical:
gcc -M --std=c89 main.c | grep termios.h | nl
1 main.o: main.c /usr/include/termios.h /usr/include/features.h
2 /usr/include/arm-linux-gnueabihf/bits/termios.h
gcc -M --std=gnu89 main.c | grep termios.h | nl
1 main.o: main.c /usr/include/termios.h /usr/include/features.h
2 /usr/include/arm-linux-gnueabihf/bits/termios.h
CRTSCTS 在定义 __USE_MISC 时在 bits/termios.h 中定义
CRTSCTS is defined in the bits/termios.h when __USE_MISC is defined
1 #ifdef __USE_MISC
2 # define CIBAUD 002003600000 /* input baud rate (not used) */
3 # define CMSPAR 010000000000 /* mark or space (stick) parity */
4 # define CRTSCTS 020000000000 /* flow control */
让我们看看 __USE_MISC.
Let's look at __USE_MISC.
gcc -M /usr/include/termios.h | nl
1 termios.o: /usr/include/termios.h /usr/include/features.h
2 /usr/include/arm-linux-gnueabihf/bits/predefs.h
3 /usr/include/arm-linux-gnueabihf/sys/cdefs.h
4 /usr/include/arm-linux-gnueabihf/bits/wordsize.h
5 /usr/include/arm-linux-gnueabihf/gnu/stubs.h
6 /usr/include/arm-linux-gnueabihf/bits/types.h
7 /usr/include/arm-linux-gnueabihf/bits/typesizes.h
8 /usr/include/arm-linux-gnueabihf/bits/termios.h
9 /usr/include/arm-linux-gnueabihf/sys/ttydefaults.h
第一个,features.h,包含 __USE_MISC 的定义,但仅当定义了 _BSD_SOURCE 或 _SVID_SOURCE 时
First one, features.h, contains definition of __USE_MISC, but only when _BSD_SOURCE or _SVID_SOURCE is defined
grep 'define __USE_MISC' /usr/include/features.h -B 1 | nl
1 #if defined _BSD_SOURCE || defined _SVID_SOURCE
2 # define __USE_MISC 1
和 _BSD_SOURCE 和 _SVID_SOURCE 在定义 _GNU_SOURCE 或 'nothing' 时定义
and _BSD_SOURCE and _SVID_SOURCE is defined when _GNU_SOURCE or 'nothing' is defined
1 #ifdef _GNU_SOURCE
2 # undef _ISOC95_SOURCE
3 # define _ISOC95_SOURCE 1
4 # undef _ISOC99_SOURCE
5 # define _ISOC99_SOURCE 1
6 # undef _POSIX_SOURCE
7 # define _POSIX_SOURCE 1
8 # undef _POSIX_C_SOURCE
9 # define _POSIX_C_SOURCE 200809L
10 # undef _XOPEN_SOURCE
11 # define _XOPEN_SOURCE 700
12 # undef _XOPEN_SOURCE_EXTENDED
13 # define _XOPEN_SOURCE_EXTENDED 1
14 # undef _LARGEFILE64_SOURCE
15 # define _LARGEFILE64_SOURCE 1
16 # undef _BSD_SOURCE
17 # define _BSD_SOURCE 1
18 # undef _SVID_SOURCE
19 # define _SVID_SOURCE 1
20 # undef _ATFILE_SOURCE
21 # define _ATFILE_SOURCE 1
22 #endif
23 /* If nothing (other than _GNU_SOURCE) is defined,
24 define _BSD_SOURCE and _SVID_SOURCE. */
25 #if (!defined __STRICT_ANSI__ && !defined _ISOC99_SOURCE &&
26 !defined _POSIX_SOURCE && !defined _POSIX_C_SOURCE &&
27 !defined _XOPEN_SOURCE && !defined _BSD_SOURCE && !defined _SVID_SOURCE)
28 # define _BSD_SOURCE 1
29 # define _SVID_SOURCE 1
30 #endif
这篇关于编译为 C99 时未定义 CRTSCTS的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!