时间戳问题

   将时间戳转换为string类型;
  1 #include <stdio.h>                           
  2 #include<iostream>
  3 #include <sstream>
  4 #include <time.h>
  5 int main ()
  6 {
  7     time_t t;
  8     struct tm * lt;
  9     time (&t);//获取Unix时间戳。
 10
 11     std::cout << t << std::endl;
 12
 13
 14  std::stringstream ss;
 15  ss << t ;
 16     std::string mytest = "abc"+ss.str();
 17
 18     std::cout << mytest << std::endl;
 19 //    lt = localtime (&t);//转为时间结构。
 20  //   printf ( "%d/%d/%d %d:%d:%d\n",lt->tm_year+1900,\
 21  //           lt->tm_mon, lt->tm_mday, lt->tm_hour, lt->tm_min, lt->tm_sec);//输出结果
 22
 23
 24     return 0;
 25 }
 



c语言将时间戳转换为字符串:struct timeval的两个属性分别是秒级和微秒级，都是long类型

头文件:
#include<sys/time.h>
char buf_temp[256];

struct timeval time;
gettimeoftoday(&time, NULL);
memset(buf_temp, sizeof(buf_temp),0x00);
sprintf(buf_temp, "%d", time.tv_sec);

// sprintf(buf_temp, "%d", time.tv_sec, tv.tv_usec / 1000);
该函数包含在stdio.h的头文件:
#include<stdio.h>
sprintd与printf函数的区别:二者功能相似,但是sprintf函数打印到字符串中,而printf函数输出在屏幕上.sprintf函数在完成其他数据转换成字符串类型的操作中应用广泛.
char str[20];
double f=14.309948;
sprintf(str,"%6.2f",f);

char str[20];
int a=20984,b=48090;
sprintf(str,"=m",a,b);
str[]="20984 48090";

测试完成的程序:
   #include<stdio.h>                                                                                                     
   #include<sys/time.h>
   #include<iostream>
   #include<cstring>
   #include<time.h>
   using namespace std;
   int main()
   {
      char buf_temp[256];
      struct timeval time;
      gettimeofday(&time, NULL);
      memset(buf_temp, sizeof(buf_temp),0x00);
      sprintf(buf_temp, "%ld%ld",time.tv_sec, time.tv_usec/1000);
      
      printf("this is a :%s\n",buf_temp);  
     
      cout << buf_temp << endl;
      return 0;
  }

printf中输出的类型:
%c:字符
%f:浮点数(包括flaot和double)
%p:指针
%s:字符串
%i:有符号十进制数
%u:无符号十进制数

使用stringstream,输出时间戳，进行封装，测试过：s（10位）;ms（13位）;us（16位）
   #include<stdio.h> 
   #include<sys/time.h>
   #include<iostream>
   #include<cstring>
   #include<time.h>
   #include <sstream>
   using namespace std;
   std::string timestampFuction()
  {
      struct timeval time;
      gettimeofday(&time, NULL);
      std::stringstream sss;
      sss << time.tv_sec;
      sss << time.tv_usec/1000;
      std::string a = sss.str();
      return a;
  }
 
 int main()
  {
       printf("++++++++++++++++++++");
       std::string ss = timestampFuction();
       printf("%s\n",ss.c_str());
       return 0;
  }          


整理好的时间戳:
static std::string timestampFuction()
{
    struct timeval time;
    gettimeofday(&time, NULL);
    std::stringstream systemTime;
    systemTime << time.tv_sec;
    systemTime << time.tv_usec/1000;
    std::string timestamp = systemTime.str();
    return timestamp;
}

C++对字符串清零.
 std::string ackContent;
 ackContent.clear();
 
 ros中的时间戳函数:
 string timestamp = std::to_string(ros::Time::now().toNSec()/1000000);
 
 ackContent.clear();


数组转换为string

解1：首地址复制
string a;
char stringarray[100];
stringarray="changestring";
a=stringarray;
解2：元素按位赋值
string a;
char stringarray[100];
stringarray="changestring";
int i=0;
while(stringarray[i]!='\0'){
a[i]=stringarray[i];
i++;
}
a[i]='\0';
解3：根据string的连接特性，粘合性
string a;
char stringarray[100];
stringarray="changestring";
a="";
int i=0;
while(stringarray[i]!='\0'){
a+=stringarray[i];//或用a,append(stringarray[i]);
i++;
}
a[i]='\0';



解决时间戳输出12位问题
 using namespace std;                                                                                                 
 static char buf_temp[256];
 std::string timestampFuction()
 {
     char buf_temp[256];
     struct timeval time;
     unsigned long ul_ms;
    gettimeofday(&time, NULL);
   //std::stringstream sss;
   //sss << time.tv_sec;
   //sss << time.tv_usec/1000;
     memset(buf_temp, sizeof(buf_temp),0x00);
     ul_ms = time.tv_sec * 1000 + time.tv_usec/1000;

      sprintf(buf_temp, "%ld",ul_ms);
   // sprintf(buf_temp, "%ld%ld",time.tv_sec, time.tv_usec/1000);
   // std::string a = sss.str();
     std::string a = buf_temp;
     return a;
  }