explain_popen

The explain_popen function is used to obtain an explanation of an error returned by the popen(3) 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:

FILE *fp = popen(command, flags);
if (!fp)
{
    fprintf(stderr, "%s\n", explain_popen(command, flags));
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_popen_or_die(3) function.

command

The original command, exactly as passed to the popen(3) system call.

flags

The original flags, exactly as passed to the popen(3) 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_popen

The explain_errno_popen function is used to obtain an explanation of an error returned by the popen(3) 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:

FILE *fp = popen(command, flags);
if (!fp)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_popen(err, command, flags));
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_popen_or_die(3) function.

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.

command

The original command, exactly as passed to the popen(3) system call.

flags

The original flags, exactly as passed to the popen(3) 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_popen

The explain_message_popen function may be used to obtain an explanation of an error returned by the popen(3) 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:

FILE *fp = popen(command, flags);
if (!fp)
{
    char message[3000];
    explain_message_popen(message, sizeof(message), command, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_popen_or_die(3) function.

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.

command

The original command, exactly as passed to the popen(3) system call.

flags

The original flags, exactly as passed to the popen(3) system call.

explain_message_errno_popen

The explain_message_errno_popen function may be used to obtain an explanation of an error returned by the popen(3) 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:

FILE *fp = popen(command, flags);
if (!fp)
{
    int err = errno;
    char message[3000];
    explain_message_errno_popen(message, sizeof(message),
        err, command, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_popen_or_die(3) function.

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.

command

The original command, exactly as passed to the popen(3) system call.

flags

The original flags, exactly as passed to the popen(3) system call.