Question

所以我在终端中使用mkfifo()功能创建了一个FIFO文件，我发送的数据为：echo"12.5 123 5 -2.1" > rndfifo

我的程序需要读取这些数字并将它们放在一个数组中，以便我以后可以使用它们。我目前只成功创建了一个程序来读取这些数字并将它们放在一个char数组中，但是我被卡住了，并且不知道如何继续这样的任何帮助？

代码：
在 16

中定义的 MSG_LEN

int main(int argc, char **argv) {
if(2 != argc)
   exit(EXIT_FAILURE); 

int fd = open(argv[1], O_RDONLY);
if(-1 == fd);
   exit(EXIT_FAILURE);

do {
    char buf[MSG_LEN];
    int bytesRead;

    if(-1 == (bytesRead = read(fd, buf,MSG_LEN))){
       perror("Reading from PIPE failed");
       exit(exit_failure);
    }
    if (0 == bytesRead)
        break;

    printf("Read number: %d\n", atoi(buf));
} while (true);

close(fd);
return 0;
}

分离我写的数字的解决方案（感谢Chintan）
（如果还有更好的那些请写出来）

如果管道发送其他东西然后是数字，我该怎么办才能停止程序？

char *deo;
float tmp;
deo = strtok(buf," ");
while(deo != NULL){
    sscanf(deo,"%f",&tmp);
    //tmp one number from buf(sent from FIFO)
    deo = strtok(NULL," ");
}

Answer 1

读完FIFO消息后，将内容放入char数组中，取出char数组并从中解析数字，或者如果还有其他数字则停止程序。 用于从char数组中读取数字 double strtod(const char *nptr, char **endptr) 要查看如何查找char数组中是否存在某些无效字符，请阅读第一个示例，然后参阅第二个（长）示例中的NOTE。

尝试使用不同字符串的以下简短示例：

char buffer[128] = "12.5 123 5 -2.1 text text 0.0 -15";

char buffer[128] = "text";

char buffer[128] = "1 2 39 3.45 0 17.3 0 10e2 78.33";

char buffer[128] = "12.5  123 5 -2.1";
char *beginPtr = buffer;
char *endPtr = NULL;
double current = 0;

while(true) 
{
    // After strtod call, if parsing was successful, 
    // endPtr will point to the first character after 
    // parsed number.
    // If no number is parsed, endPtr will not change.
    current = strtod(beginPtr, &endPtr);

    // If endPtr is unchanged from last iteration,
    // strtod encountered some non-float character
    // EOF for example
    if(beginPtr == endPtr) {
        break;
    }

    // Moving beginPtr
    beginPtr = endPtr;
    printf("%lf\n", current);
}

从FIFO消息中获取数字的平均值的更长示例。如果你需要将这些数字放在数组中，这里是如何（如果你需要取平均值，你甚至不需要将它们放在数组中:)）

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#define MAX_LEN (256)
// cond should be TRUE if there is no error
void CHECKERR(bool cond, char* msg);
void printArray(double *array, int n);

int main(int argc, char** argv)
{
    // For errno 22, perror will print 'Invalid argument'
    errno = 22;
    CHECKERR(2 == argc, "Usage: ./2 pathToFifoFile\n");
    errno = 0;

    int fileDesc = 0;
    char buffer[MAX_LEN];
    char *beginPtr = NULL;
    char *endPtr = NULL;

    double *array = NULL;        
    double current = 0.0;
    double sum = 0.0;
    double avg = 0.0;
    int count = 0;

    fileDesc = open(argv[1], O_RDONLY);
    CHECKERR(-1 != fileDesc, "Failed to open file.\n");    
    CHECKERR(-1 != read(fileDesc, buffer, sizeof buffer), "Failed to read file.\n");

    beginPtr = buffer;
    while(true) 
    {   
        // Move the endPtr if parsing was successful
        current = strtod(beginPtr, &endPtr);

        // NOTE: echo "12.5  123 5 -2.1" > /tmp/rndfifo
        // will put '\n' at the end of the string.
        // If you have regular string, change the *endPtr != '\0'
        if(beginPtr == endPtr && *endPtr != '\n')
        {
            printf("Further characters after float: %s\n", endPtr);
            errno = 22;            
            CHECKERR(false, "FIFO contains non-float characters");
        }

        if(beginPtr == endPtr) {
            break;
        }
        // Moving beginPtr
        beginPtr = endPtr;

        sum += current;
        count++;        
    }

    // Print out average
    avg = sum / count;
    printf("Average: %.2lf\n", avg);

    // At this point we know how much numbers are stored in buffer
    array = (double*)malloc(count * sizeof(double));
    CHECKERR(NULL != array, "malloc() failed.\n");

    // Go trough buffer again to put numbers in array
    beginPtr = buffer;
    int i;
    for(i = 0; i < count; i++) 
    {
        current = strtod(beginPtr, &endPtr);
        beginPtr = endPtr;
        array[i] = current;
    }

    close(fileDesc);
    printArray(array, count);
    free(array);

    return 0;
}

最后， printArray 和 CHECKERR 实施：

void printArray(double *array, int n)
{
    int i;
    for(i = 0; i < n; i++) {
        printf("%.2lf ", array[i]);
    }
    putchar('\n');
}


void CHECKERR(bool cond, char* msg)
{
    if(!cond) 
    {
        perror(msg);
        exit(EXIT_FAILURE);
    }
}

FIFO接收号码（C代码）

1 个答案: