Question

我是使用linux / raspbian编程的新手，我正在尝试创建一个程序来提取Pi系统时间，并在引脚23变高时将其写入文本文件。引脚23连接到S-R锁存器，引脚24发出复位信号以复位锁存器。

我遇到的问题是它似乎没有向创建的文本文件写任何内容。该程序创建文件正常但不写任何东西。这是我的代码：

using namespace std; 
FILE *f; 
struct timeval curTime;

int main(int argc, char *argv[]){
char dateiname[256] = "";
int i=0;
int milli;
int seconds_in_day;

wiringPiSetupGpio();

time_t t = time(0);
struct tm * now = localtime(&t);

//Create and open file
sprintf(dateiname, "/home/raspbian/Desktop/%02d%02d%02d_%02d_%02d.txt", 
                       now -> tm_year+1900, 
                       now -> tm_mon+1, 
                       now -> tm_mday, 
                       now -> tm_hour, 
                       now -> tm_min); 

f = fopen(dateiname, "w");
//write heading to file before loop
fprintf(f, "Picture, system time\n");

//Set 23 & 24 as input/ output
pinMode(23, INPUT);
pullUpDnControl(23, PUD_DOWN);
pinMode(24, OUTPUT);

while(1){ 
if(digitalRead(23)){ //If 23 is high
   i=i+1;
   gettimeofday(&curTime, NULL);
   milli = curTime.tv_usec / 1000; //Get time in milliseconds
   seconds_in_day = curTime.tv_sec % 86400; //Get seconds since midnight
   fprintf(f, "&d &d.%d\n", i, seconds_in_day, milli); //Write to file

   //send out reset signal
   digitalWrite(24, HIGH); 
   //pause for 1 second
   delay(1000);
}
}
fclose(f);
return(0);
}

有人在这里看到任何明显的错误吗？我也在终端通过

运行程序

sudo /home/raspbian/Desktop/program

退出终端窗口退出程序。感谢

Answer 1

它可能会缓冲输出。在fclose执行之前，不会写入缓冲区，这是永远不会。

如果您希望在引脚23为高电平时每秒更新一次文件，请将文件fopen和fclose放入循环中。如果您希望每秒添加一行，请在fflush(f);之后添加fprintf。

Answer 2

我怀疑引脚24上的输出需要为“短”周期“高”才能使锁存器复位，然后返回“低”以准备下次需要复位锁存器。

像while( !digitalRead(23) );这样的行会烧掉很多CPU周期，所以可能希望将一些'delay（）'或yield()放入每个循环的主体中

using namespace std;
FILE *f;
struct timeval curTime;

int main(int argc, char *argv[]){
    char dateiname[256] = "";
    int i=0;
    int milli;
    int seconds_in_day;

    wiringPiSetupGpio();

    time_t t = time(0);
    struct tm * now = localtime(&t);

    //Create and open file
    sprintf(dateiname, "/home/raspbian/Desktop/%02d%02d%02d_%02d_%02d.txt",
                           now -> tm_year+1900,
                           now -> tm_mon+1,
                           now -> tm_mday,
                           now -> tm_hour,
                           now -> tm_min);

    if( NULL == (f = fopen(dateiname, "w") )
    { // then fopen failed
        perror( "fopen failed for output file");
        exit(EXIT_FAILURE);
    }

    // implied else, fopen successful

    //write heading to file before loop
    fprintf(f, "Picture, system time\n");
    fflush( f );

    //Set 23 & 24 as input/ output
    pinMode(23, INPUT);
    pullUpDnControl(23, PUD_DOWN);
    pinMode(24, OUTPUT);

    // assure latch is reset
    digitalWrite(24, LOW);
    digitalWrite(24, HIGH);
    digitalWrite(24, LOW);

    while(1)
    {
        // wait while pin23 is low
        while( !digitalRead(23));

        // 23 is high
        i=i+1;
        gettimeofday(&curTime, NULL);
        milli = curTime.tv_usec / 1000; //Get time in milliseconds
        seconds_in_day = curTime.tv_sec % 86400; //Get seconds since midnight
        fprintf(f, "&d &d.%d\n", i, seconds_in_day, milli); //Write to file
        fflush( f );

        // if a latch 'set' signal is received during the following
        // three instructions, then could get locked into 
        // the while pin23 high loop

        // reset latch
        digitalWrite(24, HIGH);
        digitalWrite(24, LOW);

        // wait for pin 23 to be low
        while( digitalRead(23) );
    } // end while

    fclose(f);
    return(0);
}

Raspberry Pi - C程序无法写入文本文件

2 个答案: