how to write the character value from structure in

问题:

struct MemoryTag1;

typedef struct MemoryTag1{
    char a[8]= {'+','0','2','6','.','5','EA','\r'}; // setpoint temperature value
    char b[8]= {'-','0','2','4','.','5','EB','\r'};
    char c[6]= {'+','0','2','0','EC','\r'};
    }Memory1;

// This is a message structure which I want to transfer over the serial interface (RS232) and later convert into integer value. please guide me in this.

回答1:

Your syntax is a bit off - try this:

// declare Memory1 struct type to hold data

typedef struct MemoryTag1 {
    char a[9]; // setpoint temperature value
    char b[9];
    char c[7];
} Memory1;

// allocate and initialise a Memory1 struct

Memory1 m = { {'+','0','2','6','.','5','E','A','\r'},
              {'-','0','2','4','.','5','E','B','\r'},
              {'+','0','2','0','E','C','\r'} };

回答2:

Really, to be honest, I'd prefer more information. But it doesn't really matter. It only affects the method of output. If you were running this on an arduino, for instance, you could output to the serial ports as easily as:

Serial.begin(9600);
Serial.write('a');

etc, etc

As others have mentioned, there are situations in which you'd be better off using null-terminated strings. If however, you had a particular reason to do so, then I suppose you could;

#include <stdio.h>

typedef struct memoryTag1_t
{
    char a[9]; // setpoint temperature value
    char b[9];
    char c[7];
} *pMemoryTag1_t;

typedef struct memoryTag2_t
{
    char a[10]; // setpoint temperature value
    char b[10];
    char c[8];
} *pMemoryTag2_t;


void displayField1(char *field, int len)
{
    for (int i=0; i<len; i++)
    {
        if (i!=0) printf(",");
        printf("%c", field[i]);
    }printf("\n");
}

void displayField2(char *field)
{
    bool firstDone = false;
    while (*field)
    {
        if (firstDone)
            printf(",");
        else
            firstDone = true;
        printf("%c", *field++);
    }
    printf("\n");
}

int main()
{
    memoryTag1_t myMem1 =
        {
            {'+','0','2','6','.','5','E','A','\r'},
            {'-','0','2','4','.','5','E','B','\r'},
            {'+','0','2','0','E','C','\r'}
        };

    memoryTag2_t myMem2 =
        {
            "+026.5EA\r",
            "-024.5EB\r",
            "+020EC\r"
        };

    displayField1(myMem1.a, sizeof(myMem1.a));
    displayField1(myMem1.b, sizeof(myMem1.b));
    displayField1(myMem1.c, sizeof(myMem1.c));

    displayField2(myMem2.a);
    displayField2(myMem2.b);
    displayField2(myMem2.c);
}

Output: (Don't forget there's a \r printed 'after' the last comma in each line)

+,0,2,6,.,5,E,A,
-,0,2,4,.,5,E,B,
+,0,2,0,E,C,
+,0,2,6,.,5,E,A,
-,0,2,4,.,5,E,B,
+,0,2,0,E,C,

回答3:

you can not declare struct in C in this way:

it should be

typedef struct MemoryTag1{
    char a[9];
    char b[9];
    char c[7];
    }Memory1;

you can set value in the declaration of an object of this structure:

Memory1 test = {
    {'+','0','2','6','.','5','E','A','\r'},
    {'-','0','2','4','.','5','E','B','\r'},
    {'+','0','2','0','E','C','\r'}
};

If you use this bloc in each initiation of a Memory1 object so you can use macro to make it easier:

#define INIT_MEMORYTAG1 {\
    {'+','0','2','6','.','5','E','A','\r'},\
    {'-','0','2','4','.','5','E','B','\r'},\
    {'+','0','2','0','EC','\r'}\
}

and then in your declaration of a Memory1 object:

Memory1 test = INIT_MEMORYTAG1;

BTW: You can not put 'EA', 'EB', 'EC' like a 1 charachter you have to separate them to: 'E','A', 'E','B', 'E','C' and so you have to update your char array sizes in the struct definition

回答4:

That is really not C syntax.

You can't have initializers in declarations of types, that doesn't have any meaning.

You need to do it like this, to build the message:

 typedef struct {
   char a[10];
   char b[10];
   char c[8];
 } Memory1;

 int main(void)
 {
   Memory1 m1;

   strcpy(m1.a, "+026.5EA\r");
   strcpy(m1.b, "-024.5EB\r");
   strcpy(m1.c, "+020EC\r");
   return 0;
 }

Note that the above will build proper C strings in the fields of the message, i.e. there will be 0-characters acting as terminators. The sizes were too small, so I changed that.

It's trivial to ignore the terminator characters if you need to send this over some format that doesn't allow them; send each field separately.

Converting one of the fields back into integers could be done using sscanf(), for instance.