linux demo---1.汇总

一. 常用
1. 自定义打印调试信息

a.在头文件中，定义如下：
#ifdef    DEBUG
#define dbmsg(fmt, args ...) printf("%s:%s[%d]: "fmt"\n", __FILE__,__FUNCTION__, __LINE__,##args)
#else
#define dbmsg(fmt,args...)
#endif
b. 需要用到打印调试时: dbmsg("print debug info!\n");
c. 在Makefile中加上: CFLAGS= -DDEBUG
或者直接在gcc 中: gcc -DDEBUG -g -o foo foo.c

1.1 打印相关
a. int64_t 的打印
printf("%"PRId64"\n", arg);  直接用%d 或 %lld都会有警告

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>     //加上这个头文件

int main ( int argc, char *argv[] )
{
    int64_t pts = 123;
    printf("%"PRId64"\n", pts);   //跨平台的方法加印
    return EXIT_SUCCESS;
}

2. 时间相关
2.1返回当前时间的分钟

#include <time.h>
static int get_current_minute()
{
    time_t now;
    struct tm *current_time;
    int last_minute = 0;
    time(&now);
    current_time = localtime(&now);
    asctime(current_time);
    last_minute = current_time->tm_min;
    return last_minute;
}

2.2 将当前时间转为long int,精确到ms

#include <sys/time.h>
#include <stdlib.h>
long int get_now_ms_time()
{
    struct timeval start;
    long int now_time;
    gettimeofday(&start, NULL);
    now_time = start.tv_sec*1000+ start.tv_usec/1000;
    printf("cong add: now_time=%ld\n",now_time);
    return now_time;
}

这样获取两次usec之后做差就可以知道耗时了
2.3 while超时避免while死循环

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <stdlib.h>

#define SPI_READ_TIMEOUT 5000 //ms

long int get_now_ms_time()
{
        struct timeval tm;
        long int now_time;
        gettimeofday(&tm, NULL);
        now_time = tm.tv_sec*1000 + tm.tv_usec/1000;
        //printf("cong add: now_time=%ld\n",now_time);
        return now_time;
}

int main ( int argc, char *argv[] )
{
        long int old_time = get_now_ms_time();
        long int now_time;
        while(1)
        {
                usleep(1000);
                now_time = get_now_ms_time();
                if( (now_time - old_time) > SPI_READ_TIMEOUT )
                {
                        printf("spi read time out\n");
                        break;
                }
        }
        printf("now return \n");
        return EXIT_SUCCESS;
}

3.大小端测试

//0-->big_endian 1-->small endian
int checkSystem()
{
    union check
    {
        int i;
        char ch;
    }c;
    c.i = 1;
    return (c.ch == 1);
}

4. 回调函数带参数

int add(int a, int b)
{
    return a + b;
}

typedef int (*PTRADD)(int, int);

int newAdd(int a, int b, PTRADD p)
{
    return p(a, b);
}

int main()
{
    PTRADD p = add;
    int sum = newAdd(3, 3, p);
    printf("sum =%d\n", sum);

    return 0;
}

5.写文件

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
static void write_to_log(char* buf, int size)
{
    int temp_fd;
    int ret;
    temp_fd = open("temp.log", O_CREAT|O_RDWR, S_IRWXU|S_IRWXG|S_IRWXO);
    if(temp_fd < 0)
        perror("file not open!\n");
    lseek(temp_fd,0,SEEK_END);
    if((ret= write(temp_fd, buf, size)) != size)
    {
        perror("file writen error!\n");
        close(temp_fd);
    }
    close(temp_fd);
    return ;
}

6.EXIT_SUCCESS与EXIT_FAILURE的头文件
使用时需包含 stdlib.h

---

二.字符串相关
2.1 将 ”0102030405“这个字符串转为数字12345
字符串长度必为偶数,这样才能将两个字符作为16进制转为数字

int atoi_t(char* src)
{
    char l,h,ret;
    //dbmsg("src[0]=%c,src[1]=%c", src[0], src[1]);
    if((src[0]>=0x30) && (src[0]<=0x39))
    {
        h = src[0]-'0';
        //printf("h=%d\n", h);
    }else if( (src[0]>=0x41)&&(src[0]<=0x46))
    {
        h = src[0]-'A'+10;
        //printf("h=%d\n", h);
    }

    if((src[1]>=0x30) && (src[1]<=0x39))
    {
        l = src[1]-'0';
        //printf("l=%d\n", l);
    }else if( (src[1]>=0x41)&&(src[1]<=0x46))
    {
        l = src[1]-'A'+10;
        //printf("l=%d\n", l);
    }
    return (h<<4|l);
}

int hex2char(unsigned char* dst, unsigned char* src, int cnt)
{
   int i=0;
   int num=0;
   dbmsg("cnt=%d", cnt);
   if(cnt % 2)
   {
       dbmsg("can't be odd number");
       return -1;
   }
   for(i=0; i<cnt; i+=2)
   {
        dst[num++] = atoi_t((char*)(src+i));
   }
#if 0
   for(i=0; i<num; i++)
   {
       printf("%d=0x%x ", i, dst[i]);
   }
   printf("\n");
#endif
   return num;
}

2.2 将buf:0x12 0x34 0x56转为字符串123456

int char2hex(unsigned char* dst, unsigned char* src, int cnt)
{
    int i;
    if(cnt > 512)
    {
        dbmsg("char2hex too large");
        return -1;
    }
    for(i=0; i<cnt; i++)
      snprintf((char*)dst+2*i, 1024, "%02X",*(src+i));

    dst[2*cnt] = '\0';
    return 0;
}

2.3 按字符串中的逗号过滤,返回指向最后一个逗号下一个字符的首地址

char* filter_string(const char* src)
{
    char* tmp;
    char* dst = (char*)src;
    while(1)
    {
        tmp = strstr(dst, ",");
        if(NULL == tmp)
            break;
        tmp ++;
        dst = tmp;
    }
    dbmsg("dst=%s", dst);
    return dst;
}

例如src=”+EIPRUDP: 192.168.1.2,9527,1,0,00010203040506“,按照字符串中的逗号过滤
则dst=00010203040506

---

三.API使用
1.mempcpy使用

[问题]warning: incompatible implicit declaration of built-in function ‘mempcpy’ [enabled by default]
[解决]将#define _GNU_SOURCE放在头文件的最开始，当然别忘了#include <string.h>

2. open

open 不能 带O_DIRECT的解决方法
解决方法在include 之前添加
#define _GNU_SOURCE