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carraysstructtypedef
Mark
Mark

Reputation: 5028

Declare arrays with different sizes in a C typedef struct

I know how to dynamic allocate a new array with malloc. I wonder if there's a way to avoid that in this situation:

#define RX_BUFFER_SIZE    256
#define TX_BUFFER_SIZE    128

typedef struct MyBuffer 
{
    volatile uint8_t RX[RX_BUFFER_SIZE];
    volatile uint8_t TX[TX_BUFFER_SIZE];
    volatile uint16_t RX_Head;
    volatile uint16_t RX_Tail;
    volatile uint16_t TX_Head;
    volatile uint16_t TX_Tail;
} MyBuffer_t;

typedef struct MyChannel
{
    // other stuff
    MyBuffer_t buffer;
} MyChannel_t;

then in my code I create several variables like this:

MyChannel_t ch1;
MyChannel_t ch2;
MyChannel_t ch3;

but I would like to set a different sizes of the arrays for each variable. It's ok to select among a small set, i.e.:

#define RX_BUFFER_SIZE_S    32
#define TX_BUFFER_SIZE_S    16

#define RX_BUFFER_SIZE_M    128
#define TX_BUFFER_SIZE_M    64

#define RX_BUFFER_SIZE_L    256
#define TX_BUFFER_SIZE_L    128

Is there a way to achieve this without using malloc?

Upvotes: 0

Views: 91

Answers (1)

user694733
user694733

Reputation: 16043

Declare your buffers as pointers:

typedef struct MyBuffer 
{
    volatile uint8_t * RX;
    volatile uint8_t * TX;
    size_t rxSize;
    size_t txSize;
    volatile uint16_t RX_Head;
   ...

And then use separate static allocation for the buffers, and use them to initialize your object.

volatile uint8_t ch1_rx_buffer[RX_BUFFER_SIZE_S];
volatile uint8_t ch1_tx_buffer[TX_BUFFER_SIZE_S];
MyChannel_t ch1 = { 
    .buffer = {
        ch1_rx_buffer, 
        ch1_tx_buffer, 
        sizeof ch1_rx_buffer, 
        sizeof ch1_tx_buffer,
         ... 
    }
}

Upvotes: 2

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