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
