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.