linux系统编程快速定位头文件的技巧之强大的grep命令

这个技巧来自于我的实际开发碰到的：

inet_addr这个函数用于把ip地址转成网络字节序，他的原型：in_addr_t inet_addr(const char *cp);

返回值为一个in_addr_t的类型，很显然这不是一个c语言的标准数据类型，想搞清楚他到底是什么类型，肯定要找到头文件，在linux系统上，头文件一般放在/usr/include下面，但是这下面非常多的头文件，根本不知道是哪个，所以：

1，第一次：grep in_addr_t /usr/include/*.h  没有结果，说明不在/usr/include的第一层目录中

2，第二次: grep "in_addr_t" /usr/include/*/*.h， 这一次出现很多结果

/usr/include/arpa/inet.h:extern in_addr_t inet_addr (const char *__cp) __THROW;
/usr/include/arpa/inet.h:extern in_addr_t inet_lnaof (struct in_addr __in) __THROW;
/usr/include/arpa/inet.h:extern struct in_addr inet_makeaddr (in_addr_t __net, in_addr_t __host)
/usr/include/arpa/inet.h:extern in_addr_t inet_netof (struct in_addr __in) __THROW;
/usr/include/arpa/inet.h:extern in_addr_t inet_network (const char *__cp) __THROW;
/usr/include/arpa/inet.h:extern char *inet_neta (in_addr_t __net, char *__buf, size_t __len) __THROW;
/usr/include/netinet/in.h:typedef uint32_t in_addr_t;
/usr/include/netinet/in.h:    in_addr_t s_addr;
/usr/include/netinet/in.h:#define    IN_CLASSA(a)        ((((in_addr_t)(a)) & 0x80000000) == 0)
/usr/include/netinet/in.h:#define    IN_CLASSB(a)        ((((in_addr_t)(a)) & 0xc0000000) == 0x80000000)
/usr/include/netinet/in.h:#define    IN_CLASSC(a)        ((((in_addr_t)(a)) & 0xe0000000) == 0xc0000000)
/usr/include/netinet/in.h:#define    IN_CLASSD(a)        ((((in_addr_t)(a)) & 0xf0000000) == 0xe0000000)
/usr/include/netinet/in.h:#define    IN_EXPERIMENTAL(a)    ((((in_addr_t)(a)) & 0xe0000000) == 0xe0000000)
/usr/include/netinet/in.h:#define    IN_BADCLASS(a)        ((((in_addr_t)(a)) & 0xf0000000) == 0xf0000000)
/usr/include/netinet/in.h:#define    INADDR_ANY        ((in_addr_t) 0x00000000)
/usr/include/netinet/in.h:#define    INADDR_BROADCAST    ((in_addr_t) 0xffffffff)
/usr/include/netinet/in.h:#define    INADDR_NONE        ((in_addr_t) 0xffffffff)
/usr/include/netinet/in.h:# define INADDR_LOOPBACK    ((in_addr_t) 0x7f000001) /* Inet 127.0.0.1.  */
/usr/include/netinet/in.h:#define INADDR_UNSPEC_GROUP    ((in_addr_t) 0xe0000000) /* 224.0.0.0 */
/usr/include/netinet/in.h:#define INADDR_ALLHOSTS_GROUP    ((in_addr_t) 0xe0000001) /* 224.0.0.1 */
/usr/include/netinet/in.h:#define INADDR_ALLRTRS_GROUP    ((in_addr_t) 0xe0000002) /* 224.0.0.2 */
/usr/include/netinet/in.h:#define INADDR_MAX_LOCAL_GROUP  ((in_addr_t) 0xe00000ff) /* 224.0.0.255 */

3，过滤，grep "in_addr_t" /usr/include/*/*.h | grep "typedef"  

用typedef过滤一次，或者用define等关键字， 这种数据类型肯定是标准类型的别名定义，出现下面这条数据，他是uint32_t这个数据类型的别名

/usr/include/netinet/in.h:typedef uint32_t in_addr_t;

4，下一步，肯定是找uint32_t的定义类型 grep "uint32_t" /usr/include/*/*.h | grep "typedef"，出现结果:

/usr/include/drm/drm.h:typedef uint32_t __u32;
/usr/include/netinet/in.h:typedef uint32_t in_addr_t;

这不是我想要的

5，grep "uint32_t" /usr/include/*.h | grep "typedef"

/usr/include/elf.h:typedef uint32_t Elf32_Word;
/usr/include/elf.h:typedef uint32_t Elf64_Word;
/usr/include/elf.h:typedef uint32_t Elf32_Addr;
/usr/include/elf.h:typedef uint32_t Elf32_Off;
/usr/include/stdint.h:typedef unsigned int        uint32_t;

这才是我想要的, uint32_t其实是unsigned int类型

6，grep -n "uint32_t" /usr/include/stdint.h 查出数据定义所在的行号

50:#ifndef __uint32_t_defined
51:typedef unsigned int        uint32_t;
52:# define __uint32_t_defined