Prototype of modbus_fuild_dequest function

modbus-build_dequest function is a function in the libmodbus library, with its prototype being:

int modbus_build_request(modbus_t *ctx, int function, int addr, int nb, uint8_t *req);

Among them, the parameter meanings are as follows:

• ctxPointer to the modbus_t structure, indicating which Modbus context object to use.
• function: Represents the Modbus function code requested.
• addr: Indicates the address of the requested register.
• nb: Indicates the number of registers requested.
• req: Represents a buffer for storing request data. The return value of the

function is the length of the requested data. If the return value is less than 0, it indicates an error.

This function is used to construct Modbus request messages, store the message data in a buffer, and send the request message by calling the function. When constructing a request message, the parameters specify the Modbus function code of the request, the register address of the request, the number of registers requested, and the buffer for storing the request data.reqmodbus_send_raw_requestfunctionaddrnbreq