gethostent_r - Linux

Overview

gethostent_r is a versatile command used to retrieve host entries from the host database. It provides a thread-safe reentrant interface, allowing for more robust and efficient host information retrieval in multi-threaded applications.

Syntax

int gethostent_r(struct hostent *restrict result,
                char *restrict buffer,
                size_t buffersize,
                struct hostent **restrict result_ptr);

Options/Flags

None.

Examples

Simple Host Information Retrieval:

struct hostent *result;

if (gethostent_r(result, buffer, sizeof(buffer), &result_ptr) == 0) {
    printf("Host Name: %s\n", result_ptr->h_name);
    printf("IP Address: %s\n", result_ptr->h_addr_list[0]);
}

Retrieving Host Information for a Specific Domain:

char hostname[] = "www.example.com";
struct hostent *result;

if (gethostent_r(result, buffer, sizeof(buffer), &result_ptr) == 0) {
    printf("Host Name: %s\n", result_ptr->h_name);
    printf("IP Addresses: ");
    for (int i = 0; result_ptr->h_addr_list[i] != NULL; i++) {
        printf("%s ", inet_ntoa(*((struct in_addr *)result_ptr->h_addr_list[i])));
    }
    printf("\n");
}

Common Issues

• Insufficient Buffer Size: Ensure that the buffer size provided is large enough to accommodate the host information.
• Potential Multi-Threading Issues: Synchronize access to host information when using gethostent_r in multi-threaded applications.

Integration

gethostent_r can be integrated with other commands for advanced tasks, such as:

• Domain Name Resolution: Combine with gethostbyname_r to resolve hostnames to IP addresses in a thread-safe manner.
• Reverse DNS Lookup: Use with gethostbyaddr_r to perform reverse DNS lookups, mapping IP addresses to hostnames.

Related Commands

• gethostbyname_r: Retrieve host information for a specific domain.
• gethostbyaddr_r: Perform reverse DNS lookups.
• gethostbyname2_r: Retrieve host information for a specific domain, supporting IPv4 and IPv6 addresses.