getnetent_r - Linux

Overview

getnetent_r is a C library function that retrieves the next network entry from the network database. It is primarily used to iterate through and retrieve information about network protocols and services.

Syntax

int getnetent_r(struct netent *netent, char *buffer, size_t buflen, struct netent **result);

Parameters

• netent: A pointer to a struct netent to store the retrieved network entry.
• buffer: A character buffer to store the network entry data.
• buflen: The size of the buffer in bytes.
• result: A pointer to a pointer to the retrieved network entry.

Options/Flags

None

Examples

Simple Usage:

struct netent *netent;
char buffer[1024];
struct netent *result;

while (getnetent_r(netent, buffer, sizeof(buffer), &result) == 0) {
    printf("Protocol: %s\n", result->n_proto);
    printf("Name: %s\n", result->n_name);
    printf("Port number: %d\n", result->n_port);
}

Complex Usage:

struct netent *netent;
char buffer[1024];
struct netent *result;

int found = 0;
while (getnetent_r(netent, buffer, sizeof(buffer), &result) == 0) {
    if (strcmp(result->n_name, "ftp") == 0) {
        printf("FTP port number: %d\n", result->n_port);
        found = 1;
        break;
    }
}

if (!found) {
    printf("FTP not found in the network database.\n");
}

Common Issues

• Null buffer: Ensure that the buffer argument is not null.
• Insufficient buffer size: The buflen argument must be large enough to store the network entry data.
• Network database not found: The network database may not be available or in the expected location.

Integration

getnetent_r can be used with other network-related commands, such as gethostbyname and getservbyname, to obtain detailed information about hosts and services on a network.

Related Commands

• gethostbyname: Retrieves host information by hostname.
• getservbyname: Retrieves service information by service name.
• getprotobyname: Retrieves protocol information by protocol name.