在嵌入式开发中，熟练掌握一些通用且高效的代码片段能极大提升开发效率和程序的健壮性。本文将分享并解析8个实用的C语言代码片段，涵盖结构体操作、系统信息获取、文件处理及日志输出等多个常见场景。
快速获取结构体成员大小及偏移量
在涉及内存布局分析或序列化时，快速获取结构体成员的大小和偏移量非常有用。最简洁的方式是通过宏定义来实现。
代码：
// 微信公众号：嵌入式大杂烩
#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
在程序异常或分析系统状态时，CPU温度是一个重要参考指标。我们可以通过读取Linux系统的温度文件来获取。
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
在文件传输或处理前，获取文件大小是常见的需求。例如，发送文件内容前需要知道数据量。
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
在日志输出或性能分析时，一个精确的时间戳至关重要。我们可以获取系统当前毫秒级时间戳。
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地址
MAC地址常被用作设备的唯一标识。通过 网络/系统 编程接口可以轻松获取。
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地址
同样，获取本机IP地址用于显示或网络配置也是很常见的功能。
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：
文件读写操作
文件操作是基础功能，将其封装成通用函数可以提高代码复用率。
代码：
// 微信公众号：嵌入式大杂烩
#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：
进度条显示
在文件传输、数据处理等耗时操作中，一个进度条能直观地反馈当前进度，提升用户体验。
代码：
// 微信公众号：嵌入式大杂烩
#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：
格式化日志输出
一个良好的日志系统是调试和定位问题的利器。一个简单的宏定义可以让日志输出带上文件名、行号和函数名等信息。
代码：
// 微信公众号：嵌入式大杂烩
#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：
开启核心转储（Core Dump）以辅助调试
程序崩溃时，生成core文件是定位问题的有效手段。以下代码片段演示了如何在Linux环境下使能core dump。
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;
}
以上便是嵌入式C语言开发中几个非常实用的代码片段，覆盖了日常开发的多个方面。熟练运用这些技巧，能让你在解决实际问题时事半功倍。如果你对 C/C++ 编程有更多兴趣，欢迎到 云栈社区 与其他开发者交流探讨。
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