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快速获取结构体成员大小及偏移量
获取结构体成员大小及偏移量的方式有多种。最简便的方式：
代码：
// 微信公众号：一起学嵌入式
#include <stdio.h>
// 获取结构体成员大小
#define GET_MEMBER_SIZE(type, member) sizeof(((type*)0)->member)
// 获取结构体成员偏移量
#define GET_MEMBER_OFFSET(type, member) ((size_t)(&(((type*)0)->member)))
typedef struct _test_struct0
{
char x;
char y;
char z;
}test_struct0;
typedef struct _test_struct1
{
char a;
char c;
short b;
int d;
test_struct0 e;
}test_struct1;
int main(int arc, char *argv[])
{
printf("GET_MEMBER_SIZE(test_struct1, a) = %ld\n", GET_MEMBER_SIZE(test_struct1, a));
printf("GET_MEMBER_SIZE(test_struct1, c) = %ld\n", GET_MEMBER_SIZE(test_struct1, c));
printf("GET_MEMBER_SIZE(test_struct1, b) = %ld\n", GET_MEMBER_SIZE(test_struct1, b));
printf("GET_MEMBER_SIZE(test_struct1, d) = %ld\n", GET_MEMBER_SIZE(test_struct1, d));
printf("GET_MEMBER_SIZE(test_struct1, e) = %ld\n", GET_MEMBER_SIZE(test_struct1, e));
printf("test_struct1 size = %ld\n", sizeof(test_struct1));
printf("GET_MEMBER_OFFSET(a): %ld\n", GET_MEMBER_OFFSET(test_struct1, a));
printf("GET_MEMBER_OFFSET(c): %ld\n", GET_MEMBER_OFFSET(test_struct1, c));
printf("GET_MEMBER_OFFSET(b): %ld\n", GET_MEMBER_OFFSET(test_struct1, b));
printf("GET_MEMBER_OFFSET(d): %ld\n", GET_MEMBER_OFFSET(test_struct1, d));
printf("GET_MEMBER_OFFSET(e): %ld\n", GET_MEMBER_OFFSET(test_struct1, e));
return 0;
}
运行结果：
获取CPU温度
应用可以定时获取CPU的温度，比如程序异常崩溃时，我们可能需要分析多方面原因，CPU温度就是其中之一。
代码：
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#define CPU_TEMP_FILE0 "/sys/devices/virtual/thermal/thermal_zone0/temp"
struct cpu_temperature
{
int integer_part;
int decimal_part;
};
typedef struct cpu_temperature cpu_temperature_t;
cpu_temperature_t get_cpu_temperature(const char *_cpu_temp_file)
{
FILE *fp = NULL;
cpu_temperature_t cpu_temperature = {0};
int temp = 0;
fp = fopen(_cpu_temp_file, "r");
if (NULL == fp)
{
printf("fopen file error\n");
return cpu_temperature;
}
fscanf(fp, "%d", &temp);
cpu_temperature.integer_part = temp / 1000;
cpu_temperature.decimal_part = temp % 1000 / 100;
fclose(fp);
return cpu_temperature;
}
int main(int arc, char *argv[])
{
cpu_temperature_t cpu_temperature = {0};
cpu_temperature = get_cpu_temperature(CPU_TEMP_FILE0);
printf("cpu_temperature = %d.%d ℃\n", cpu_temperature.integer_part, cpu_temperature.decimal_part);
return 0;
}
运行结果：
获取文件大小
有时候我们需要获取某个文件的大小，比如如果需要发送文件里的内容，则需要知道文件的大小。
代码：
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
long get_file_size(const char *_file_name)
{
FILE * fp = fopen(_file_name, "r");
if (NULL == fp)
{
printf("fopen error\n");
return -1;
}
fseek(fp, 0L, SEEK_END);
long size = ftell(fp);
fclose(fp);
return size;
}
int main()
{
#define FILE_NAME "./get_file_size"
long file_size = get_file_size(FILE_NAME);
printf("file_size = %ld\n", file_size);
return 0;
}
运行结果：
获取时间戳
系统时间戳很常用，比如log输出时，可以附带时间戳数据，方便分析。
代码：
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <time.h>
long long get_sys_time_ms(void)
{
long long time_ms = 0;
struct timeval sys_current_time;
gettimeofday(&sys_current_time, NULL);
time_ms = ((long long)sys_current_time.tv_sec*1000000 + sys_current_time.tv_usec) / 1000;
return time_ms;
}
int main(int arc, char *argv[])
{
long long cur_sys_time = get_sys_time_ms();
printf("cur_sys_time = %lld ms\n", cur_sys_time);
return 0;
}
运行结果：
获取MAC
MAC地址，有时候会作为设备ID实用，作为设备唯一标识。
代码：
#include <stdio.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
int get_netif_mac(const char *_ifr_name, uint8_t *_mac)
{
int32_t ret = -1;
struct ifreq m_ifreq;
int32_t sock = 0;
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0)
{
printf("socket err\r\n");
goto err;
}
strcpy(m_ifreq.ifr_name, _ifr_name);
ret = ioctl(sock,SIOCGIFHWADDR, &m_ifreq);
if (ret < 0)
{
printf("ioctl err:%d\r\n",ret);
goto err;
}
snprintf((char *)_mac, 32, "%02x%02x%02x%02x%02x%02x", (uint8_t)m_ifreq.ifr_hwaddr.sa_data[0],
(uint8_t)m_ifreq.ifr_hwaddr.sa_data[1],
(uint8_t)m_ifreq.ifr_hwaddr.sa_data[2],
(uint8_t)m_ifreq.ifr_hwaddr.sa_data[3],
(uint8_t)m_ifreq.ifr_hwaddr.sa_data[4],
(uint8_t)m_ifreq.ifr_hwaddr.sa_data[5]);
return 0;
err:
return -1;
}
int main(int argc, char **argv)
{
char mac_str[32] = {0};
get_netif_mac("wlan1", mac_str);
printf("mac = %s\n", mac_str);
return 0;
}
运行结果：
获取IP
有时候需要获取本机IP进行显示。
代码：
#include <stdio.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
int get_local_ip(const char *_ifr_name, char *_ip)
{
int ret = -1;
int sockfd;
struct sockaddr_in sin;
struct ifreq ifr;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (-1 == sockfd)
{
printf("socket error\n");
return ret;
}
strncpy(ifr.ifr_name, _ifr_name, IFNAMSIZ);
ifr.ifr_name[IFNAMSIZ - 1] = 0;
if (ioctl(sockfd, SIOCGIFADDR, &ifr) < 0)
{
printf("ioctl error\n");
close(sockfd);
return ret;
}
memcpy(&sin, &ifr.ifr_addr, sizeof(sin));
int ip_len = snprintf(_ip, 32, "%s", inet_ntoa(sin.sin_addr));
close(sockfd);
ret = ip_len;
return ret;
}
int main(int argc, char **argv)
{
char ip_str[32] = {0};
get_local_ip("wlan1", ip_str);
printf("ip = %s\n", ip_str);
return 0;
}
运行结果：
文件操作
文件操作平时用得很多，为了方便使用，可以自己根据实际需要再封装一层：
代码：
// 微信公众号：一起学嵌入式
#include <stdio.h>
static int file_opt_write(const char *filename, void *ptr, int size)
{
FILE *fp;
size_t num;
fp = fopen(filename, "wb");
if(NULL == fp)
{
printf("open %s file error!\n", filename);
return -1;
}
num = fwrite(ptr, 1, size, fp);
if(num != size)
{
fclose(fp);
printf("write %s file error!\n", filename);
return -1;
}
fclose(fp);
return num;
}
static int file_opt_read(const char *filename, void *ptr, int size)
{
FILE *fp;
size_t num;
fp = fopen(filename, "rb");
if(NULL == fp)
{
printf("open %s file error!\n", filename);
return -1;
}
num = fread(ptr, 1, size, fp);
if(num != size)
{
fclose(fp);
printf("write %s file error!\n", filename);
return -1;
}
fclose(fp);
return num;
}
typedef struct _test_struct
{
char a;
char c;
short b;
int d;
}test_struct;
int main(int arc, char *argv[])
{
#define FILE_NAME "./test_file"
test_struct write_data = {0};
write_data.a = 1;
write_data.b = 2;
write_data.c = 3;
write_data.d = 4;
printf("write_data.a = %d\n", write_data.a);
printf("write_data.b = %d\n", write_data.b);
printf("write_data.c = %d\n", write_data.c);
printf("write_data.d = %d\n", write_data.d);
file_opt_write(FILE_NAME, (test_struct*)&write_data, sizeof(test_struct));
test_struct read_data = {0};
file_opt_read(FILE_NAME, (test_struct*)&read_data, sizeof(test_struct));
printf("read_data.a = %d\n", read_data.a);
printf("read_data.b = %d\n", read_data.b);
printf("read_data.c = %d\n", read_data.c);
printf("read_data.d = %d\n", read_data.d);
return 0;
}
运行结果：
进度条
有时候，加上进度条可以比较方便知道当前的下载进度、写入文件的进度等。
代码：
// 微信公众号：一起学嵌入式
#include <stdio.h>
#include <string.h>
#include <unistd.h>
typedef struct _progress
{
int cur_size;
int sum_size;
}progress_t;
void progress_bar(progress_t *progress_data)
{
int percentage = 0;
int cnt = 0;
char proc[102];
memset(proc, '\0', sizeof(proc));
percentage = (int)(progress_data->cur_size * 100 / progress_data->sum_size);
printf("percentage = %d %%\n", percentage);
if (percentage <= 100)
{
while (cnt <= percentage)
{
printf("[%-100s] [%d%%]\r", proc, cnt);
fflush(stdout);
proc[cnt] = '#';
usleep(100000);
cnt++;
}
}
printf("\n");
}
int main(int arc, char *argv[])
{
progress_t progress_test = {0};
progress_test.cur_size = 65;
progress_test.sum_size = 100;
progress_bar(&progress_test);
return 0;
}
运行结果：
日志输出
日志输出常常需要带一些格式。最简单的方式如：
代码：
// 微信公众号：一起学嵌入式
#include <stdio.h>
#define LOG_D(fmt, args...) do\
{\
printf("<<File:%s Line:%d Function:%s>> ", __FILE__, __LINE__, __FUNCTION__);\
printf(fmt, ##args);\
}while(0)
int main(int arc, char *argv[])
{
char ch = 'a';
char str[10] = "ZhengN";
float float_val = 10.10;
int num = 88;
double double_val = 10.123456;
LOG_D("字符为 %c \n", ch);
LOG_D("字符串为 %s \n" , str);
LOG_D("浮点数为 %f \n", float_val);
LOG_D("整数为 %d\n" , num);
LOG_D("双精度值为 %lf \n", double_val);
LOG_D("八进制值为 %o \n", num);
LOG_D("十六进制值为 %x \n", num);
return 0;
}
运行结果：
后台运行生成core文件
代码：
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/resource.h>
#define SHELL_CMD_CONF_CORE_FILE "echo /var/core-%e-%p-%t > /proc/sys/kernel/core_pattern"
#define SHELL_CMD_DEL_CORE_FILE "rm -f /var/core*"
static int enable_core_dump(void)
{
int ret = -1;
int resource = RLIMIT_CORE;
struct rlimit rlim;
rlim.rlim_cur = 1 ? RLIM_INFINITY : 0;
rlim.rlim_max = 1 ? RLIM_INFINITY : 0;
system(SHELL_CMD_DEL_CORE_FILE);
if (0 != setrlimit(resource, &rlim))
{
printf("setrlimit error!\n");
return -1;
}
else
{
system(SHELL_CMD_CONF_CORE_FILE);
printf("SHELL_CMD_CONF_CORE_FILE\n");
return 0;
}
return ret;
}
int main(int argc, char **argv)
{
enable_core_dump();
printf("==================segmentation fault test==================\n");
int *p = NULL;
*p = 1234;
return 0;
}
以上就是本次分享的几个小的代码片段。
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