选择库文件
#pragma comment(lib,"ws2_32.lib")几个主要的函数
#include <stdio.h>#ifndef _MSC_VER#include <unistd.h>#endif#include <string.h>#include <stdlib.h>#include <errno.h>#include <modbus.h>#pragma comment(lib,"ws2_32.lib")#if defined(_WIN32)#define close closesocket#endifenum { TCP, RTU};int main(int argc, char argv[]){ int s = -1; modbus_t ctx = NULL; modbus_mapping_t mb_mapping = NULL; //寄存器管理 int rc; int use_backend; / TCP / if (argc > 1) { if (strcmp(argv[1], "tcp") == 0) { use_backend = TCP; } else if (strcmp(argv[1], "rtu") == 0) { use_backend = RTU; } else { printf("Usage:\n %s [tcp|rtu] - Modbus client to measure data bandwidth\n\n", argv[0]); exit(1); } } else { / By default / use_backend = TCP; } if (use_backend == TCP) { ctx = modbus_new_tcp("127.0.0.1", 1502); //监听端口，默认是502 s = modbus_tcp_listen(ctx, 1); modbus_tcp_accept(ctx, &s); } else { ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1); modbus_set_slave(ctx, 1); modbus_connect(ctx); }//这个要重点关注，设置寄存器和线圈的个数，起始地址为0，//如果不想从0开始，可以用这个方法modbus_mapping_new_start_address mb_mapping = modbus_mapping_new(MODBUS_MAX_READ_BITS, 0, MODBUS_MAX_READ_REGISTERS, 0); if (mb_mapping == NULL) { fprintf(stderr, "Failed to allocate the mapping: %s\n", modbus_strerror(errno)); modbus_free(ctx); return -1; }//modbus的数据收发 for(;;) { uint8_t query[MODBUS_TCP_MAX_ADU_LENGTH]; rc = modbus_receive(ctx, query); if (rc > 0) { modbus_reply(ctx, query, rc, mb_mapping); } else if (rc == -1) { / Connection closed by the client or error / break; } } printf("Quit the loop: %s\n", modbus_strerror(errno)); modbus_mapping_free(mb_mapping); if (s != -1) { close(s); } / For RTU, skipped by TCP (no TCP connect) / modbus_close(ctx); modbus_free(ctx); return 0;}如何与运用结合。modbus_mapping_t 构造体里面存储了所有的寄存器和线圈，只须要将运用的值更新到里面就可以，通过读取保持寄存器就可以获取Monster写入的值。
typedef struct _modbus_mapping_t { int nb_bits; int start_bits; int nb_input_bits; int start_input_bits; int nb_input_registers; int start_input_registers; int nb_registers; int start_registers; uint8_t tab_bits; //线圈寄存器 uint8_t tab_input_bits; //输入线圈寄存器 uint16_t tab_input_registers; //输入寄存器 uint16_t tab_registers; //保持寄存器} modbus_mapping_t;
