---
name: "explain_connect"
section: "3"
platform: "linux"
package: "libexplain-dev"
version: "1.4.D001-16"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/explain_connect"
---

# explain\_connect(3)

explain connect(2) errors

## NAME

explain\_connect - explain [connect(2)](/connect/2.md) errors

## SYNOPSIS

\#include \<libexplain/connect.h\>

const char \*explain\_connect(int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);\
 const char \*explain\_errno\_connect(int errnum, int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);\
 void explain\_message\_connect(char \*message, int message\_size, int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);\
 void explain\_message\_errno\_connect(char \*message, int message\_size, int errnum, int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);

## DESCRIPTION

These functions may be used to obtain explanations for errors returned by the [*connect*(2)](/connect/2.md) system call.

### explain\_connect

const char \*explain\_connect(int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);

The **explain\_connect** function is used to obtain an explanation of an error returned by the [*connect*(2)](/connect/2.md) system call.  The least the message will contain is the value of `strerror(errno)`, but usually it will do much better, and indicate the underlying cause in more detail.

The *errno* global variable will be used to obtain the error value to be decoded.

This function is intended to be used in a fashion similar to the following example:

```
if (connect(fildes, serv_addr, serv_addr_size) < 0)
{
    fprintf(stderr, "%s\n", explain_connect(fildes, serv_addr,
        serv_addr_size));
    exit(EXIT_FAILURE);
}
```

- *fildes*

  The original fildes, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr*

  The original serv\_addr, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr\_size*

  The original serv\_addr\_size, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- Returns:

  The message explaining the error.  This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list.  This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

**Note:** This function is **not** thread safe, because it shares a return buffer across all threads, and many other functions in this library.

### explain\_errno\_connect

const char \*explain\_errno\_connect(int errnum, int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);

The **explain\_errno\_connect** function is used to obtain an explanation of an error returned by the [*connect*(2)](/connect/2.md) system call. The least the message will contain is the value of `strerror(errnum)`, but usually it will do much better, and indicate the underlying cause in more detail.

This function is intended to be used in a fashion similar to the following example:

```
if (connect(fildes, serv_addr, serv_addr_size) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_connect(err,
        fildes, serv_addr, serv_addr_size));
    exit(EXIT_FAILURE);
}
```

- *errnum*

  The error value to be decoded, usually obtained from the *errno* global variable just before this function is called.  This is necessary if you need to call **any** code between the system call to be explained and this function, because many libc functions will alter the value of *errno*.

- *fildes*

  The original fildes, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr*

  The original serv\_addr, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr\_size*

  The original serv\_addr\_size, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- Returns:

  The message explaining the error.  This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list.  This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

**Note:** This function is **not** thread safe, because it shares a return buffer across all threads, and many other functions in this library.

### explain\_message\_connect

void explain\_message\_connect(char \*message, int message\_size, int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);

The **explain\_message\_connect** function may be used to  obtain an explanation of an error returned by the [*connect*(2)](/connect/2.md) system call. The least the message will contain is the value of `strerror(errno)`, but usually it will do much better, and indicate the underlying cause in more detail.

The *errno* global variable will be used to obtain the error value to be decoded.

This function is intended to be used in a fashion similar to the following example:

```
if (connect(fildes, serv_addr, serv_addr_size) < 0)
{
    char message[3000];
    explain_message_connect(message, sizeof(message),
        fildes, serv_addr, serv_addr_size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

- *message*

  The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

- *message\_size*

  The size in bytes of the location in which to store the returned message.

- *fildes*

  The original fildes, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr*

  The original serv\_addr, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr\_size*

  The original serv\_addr\_size, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

### explain\_message\_errno\_connect

void explain\_message\_errno\_connect(char \*message, int message\_size, int errnum, int fildes, const struct sockaddr \*serv\_addr, int serv\_addr\_size);

The **explain\_message\_errno\_connect** function may be used to obtain an explanation of an error returned by the [*connect*(2)](/connect/2.md) system call. The least the message will contain is the value of `strerror(errnum)`, but usually it will do much better, and indicate the underlying cause in more detail.

This function is intended to be used in a fashion similar to the following example:

```
if (connect(fildes, serv_addr, serv_addr_size) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_connect(message, sizeof(message), err,
        fildes, serv_addr, serv_addr_size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

- *message*

  The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

- *message\_size*

  The size in bytes of the location in which to store the returned message.

- *errnum*

  The error value to be decoded, usually obtained from the *errno* global variable just before this function is called.  This is necessary if you need to call **any** code between the system call to be explained and this function, because many libc functions will alter the value of *errno*.

- *fildes*

  The original fildes, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr*

  The original serv\_addr, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

- *serv\_addr\_size*

  The original serv\_addr\_size, exactly as passed to the [*connect*(2)](/connect/2.md) system call.

## SEE ALSO

- [*connect*(2)](/connect/2.md)

  initiate a connection on a socket

- [*explain\_connect\_or\_die*(3)](/explain_connect_or_die/3.md)

  initiate a connection on a socket and report errors

## COPYRIGHT

libexplain version 1.4\
 Copyright (C) 2008 Peter Miller