Raspberry Pi - C 程序不写入文本文件

Question

我是使用 linux/raspbian 编程的新手，我正在尝试制作一个程序来提取 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入任何内容。该程序可以很好地创建文件，但不会向其中写入任何内容。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);
}

有人看到这里有什么明显的错误吗？我也是运行终端里的程序通过

sudo /home/raspbian/Desktop/program

并通过退出终端 window 来退出程序。谢谢

Answer 1

它可能正在缓冲输出。在 fclose 执行之前，缓冲区不一定会被写入，而这永远不会。

如果您希望文件在 23 号针为高电平时每秒更新一次单行，请将文件 fopen 和 fclose 放入循环中。如果你想每秒添加一行，那么在fprintf之后添加fflush(f);。

Answer 2

我怀疑引脚 24 上的输出需要 'short' 周期 'high' 才能使锁存器复位，然后是 return 到 'low'为下次需要重置锁存器做准备。

像这样的行：while( !digitalRead(23) ); 会燃烧很多 CPU 周期，因此可能需要将一些 'delay()' 或 yield() 放入每个周期的正文中循环

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 程序不写入文本文件

Raspberry Pi - C program not writing to text file

c

linux

io

raspbian