---
name: "modbus_read_registers"
section: "3"
platform: "linux"
package: "libmodbus-dev"
version: "3.1.6-2.1"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/modbus_read_registers"
---

# modbus\_read\_registers(3)

read many registers

## NAME

modbus\_read\_registers - read many registers

## SYNOPSIS

**int modbus\_read\_registers(modbus\_t \****ctx***, int** *addr***, int** *nb***, uint16\_t \****dest***);**

## DESCRIPTION

The **modbus\_read\_registers()** function shall read the content of the *nb* holding registers to the address *addr* of the remote device. The result of reading is stored in *dest* array as word values (16 bits).

You must take care to allocate enough memory to store the results in *dest* (at least *nb* \* sizeof(uint16\_t)).

The function uses the Modbus function code 0x03 (read holding registers).

## RETURN VALUE

The function shall return the number of read registers if successful. Otherwise it shall return -1 and set errno.

## ERRORS

**EMBMDATA**

Too many registers requested

## EXAMPLE

```
modbus_t *ctx;
uint16_t tab_reg[64];
int rc;
int i;
ctx = modbus_new_tcp("127.0.0.1", 1502);
if (modbus_connect(ctx) == -1) {
    fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
    modbus_free(ctx);
    return -1;
}
rc = modbus_read_registers(ctx, 0, 10, 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);
```

## SEE ALSO

[**modbus\_write\_register**(3)](/modbus_write_register/3.md) [**modbus\_write\_registers**(3)](/modbus_write_registers/3.md)

## AUTHORS

The libmodbus documentation was written by Stéphane Raimbault \<stephane.raimbault@gmail.com\>