Define and use a char string in the struct

Question

I want to build a struct and contains int and char variables. Here is my code:

typedef struct {
        uint16_t type;      
        uint16_t sn;
        int data1;
        int data2;
        char crc[1024];
    }packet_t;

Then I use a method to create a struct:

packet_t packetCreate(uint16_t type,uint16_t sn, uint16_t data1, 
uint16_t data2, char crc[1024])
{
    packet_t packet;
    packet.type = type;
    packet.sn = sn; 
    packet.data1 = data1;
    packet.data2 = data2;
    packet.crc = crcr;
    return packet;
}

Also I have defined the corresponding variables in the code. But when I compile the code it doesn't work and displays:

incompatible types when assigning to type ‘char[1024]’ from type ‘char *’ in the line: packet.crc = crcr; How should I define and use the struct? I want to build the struct contains a char string, so I can store the CRC strings of data.

should the line be packet.crc = crc; instead of packet.crc = crcr; — tom
– tom, Commented Apr 23, 2016 at 15:54
See: stackoverflow.com/a/16645642/817132 Or K&R's C, page 97: ime.usp.br/~pf/Kernighan-Ritchie/C-Programming-Ebook.pdf — wally
– wally, Commented Apr 23, 2016 at 16:08

Pavan · Accepted Answer · 2016-04-23 15:53:54Z

3

You cant just assign string to another string.Like

packet.crc = crc;

The above method is wrong. You need to use command strcpy here from library string.

strcpy(packet.crc,crc);

Don't forget to call library string.h.

answered Apr 23, 2016 at 15:53

Pavan

2503 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

too honest for this site Over a year ago

Note: C does not have a string type. It is all convention. And they are not the same types anyway. The member is an array, the paramter is a pointer.

Ed Heal · Accepted Answer · 2016-04-23 16:06:10Z

3

Use memcpy. i.e.

memcpy(packet.crc, crc, sizeof(packet.crc));

To copy the contents into the array.

You need

#include <string.h>

to use this function

edited Apr 23, 2016 at 16:06

answered Apr 23, 2016 at 15:50

Ed Heal

60.3k18 gold badges91 silver badges137 bronze badges

1 Comment

tom Over a year ago

NB missing comma - should be memcpy(packet.crc, crc, sizeof(packet.crc)); - I can't try to edit this in because I need to put at least 6 characters in for that

Yağmur Oymak · Accepted Answer · 2016-04-23 15:55:52Z

2

You can not directly assign arrays to each other. You may use library functions like memcpy(), (or strcpy() in the case of a null terminated string). Another way is to copy the elements from the source array to the destination one by one by a loop.

answered Apr 23, 2016 at 15:55

Yağmur Oymak

4874 silver badges14 bronze badges

Comments

Spikatrix · Accepted Answer · 2016-04-23 16:19:37Z

2

In addition to the other comments I am concerned that you define your packet_t variable packet inside the function and when the function returns the memory allocated to packet will 'disappear'.

It is better to declare packet in main and then call the routine with the address of packet - or the pointer to packet.

You can then change your function to

void packetCreate(packet_t *p_packet, ruint16_t type,uint16_t sn, uint16_t data1, 
uint16_t data2, char crc[1024])
{
   // p_packetn =  &packet - it is a pointer to the packet
    p_packet->type = type;
    p_packet->sn = sn; 
    p_packet->data1 = data1;
    p_packet->data2 = data2;
    p_packet->crc = crcr; // note other answers to correct this line
    return ;
}

edited Apr 23, 2016 at 16:19

Spikatrix

20.3k7 gold badges44 silver badges85 bronze badges

answered Apr 23, 2016 at 15:57

tom

1,32310 silver badges17 bronze badges

Collectives™ on Stack Overflow

Define and use a char string in the struct

4 Answers 4

1 Comment

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related