libmodbus

#include <modbus.h>
modbus_t *ctx;
uint16_t tab_reg[64];
int rc;
int i;
int main(void) {

	ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);

	if (ctx == NULL) {
		  fprintf(stderr, "Unable to create the libmodbus context\n");
		  return -1;
	}
	rc = modbus_read_registers(ctx, 2, 3, tab_reg);

	if (rc == -1) {
		  fprintf(stderr, "%s\n", modbus_strerror(errno));
		  return -1;
	}

	for (i=0; i < rc; i++) {
		  printf("reg[%d]=%d (0x%X)\n", i, tab_reg[i], tab_reg[i]);
	}

	modbus_close(ctx);
	modbus_free(ctx);
}



# apt-get install libmodbus5 libmodbus-dev

$ gcc test.c -o test
test.c:1:20: fatal error: modbus.h: File not found
 #include <modbus.h>
                    ^
compilation terminated.





$ gcc -I /usr/include/modbus -o test test.c
test.c:9:1: warning: data definition has no type or storage class [enabled by default]
 ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);
 ^
test.c:9:1: error: conflicting types for ‘ctx’
test.c:2:11: note: previous declaration of ‘ctx’ was here
 modbus_t *ctx;
           ^
test.c:9:7: warning: initialization makes integer from pointer without a cast [enabled by default]
 ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);
       ^
test.c:9:1: error: initializer element is not constant
 ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);
 ^
test.c:11:1: error: expected identifier or ‘(’ before ‘if’
 if (ctx == NULL) {
 ^
test.c:17:1: warning: data definition has no type or storage class [enabled by default]
 rc = modbus_read_registers(ctx, 2, 3, tab_reg);
 ^
test.c:17:1: warning: passing argument 1 of ‘modbus_read_registers’ makes pointer from integer without a cast [enabled by default]
In file included from test.c:1:0:
/usr/include/modbus/modbus.h:170:5: note: expected ‘struct modbus_t *’ but argument is of type ‘int’
 int modbus_read_registers(modbus_t *ctx, int addr, int nb, uint16_t *dest);
     ^
test.c:17:1: error: initializer element is not constant
 rc = modbus_read_registers(ctx, 2, 3, tab_reg);
 ^
test.c:19:1: error: expected identifier or ‘(’ before ‘if’
 if (rc == -1) {
 ^
test.c:24:1: error: expected identifier or ‘(’ before ‘for’
 for (i=0; i < rc; i++) {
 ^
test.c:24:13: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘<’ token
 for (i=0; i < rc; i++) {
             ^
test.c:24:20: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘++’ token
 for (i=0; i < rc; i++) {
                    ^
test.c:28:1: warning: data definition has no type or storage class [enabled by default]
 modbus_close(ctx);
 ^
test.c:28:1: warning: parameter names (without types) in function declaration [enabled by default]
test.c:28:1: error: conflicting types for ‘modbus_close’
In file included from test.c:1:0:
/usr/include/modbus/modbus.h:159:6: note: previous declaration of ‘modbus_close’ was here
 void modbus_close(modbus_t *ctx);
      ^
test.c:29:1: warning: data definition has no type or storage class [enabled by default]
 modbus_free(ctx);
 ^
test.c:29:1: warning: parameter names (without types) in function declaration [enabled by default]
test.c:29:1: error: conflicting types for ‘modbus_free’
In file included from test.c:1:0:
/usr/include/modbus/modbus.h:161:6: note: previous declaration of ‘modbus_free’ was here
 void modbus_free(modbus_t *ctx);
      ^


$ lsb_release -a
No LSB modules are available.
Distributor ID:	LinuxMint
Description:	Linux Mint 16 Petra
Release:	16
Codename:	petra
$