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

# explain\_realpath(3)

explain realpath(3) errors

## NAME

explain\_realpath - explain [*realpath*(3)](/realpath/3.md) errors

## SYNOPSIS

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

const char \*explain\_realpath(const char \*pathname, char \*resolved\_pathname);\
 const char \*explain\_errno\_realpath(int errnum, const char \*pathname, char \*resolved\_pathname);\
 void explain\_message\_realpath(char \*message, int message\_size, const char \*pathname, char \*resolved\_pathname);\
 void explain\_message\_errno\_realpath(char \*message, int message\_size, int errnum, const char \*pathname, char \*resolved\_pathname);

## DESCRIPTION

These functions may be used to obtain explanations for errors returned by the [*realpath*(3)](/realpath/3.md) system call.

### explain\_realpath

const char \*explain\_realpath(const char \*pathname, char \*resolved\_pathname);

The **explain\_realpath** function is used to obtain an explanation of an error returned by the [*realpath*(3)](/realpath/3.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.

- *pathname*

  The original pathname, exactly as passed to the [*realpath*(3)](/realpath/3.md) system call.

- *resolved\_pathname*

  The original resolved\_pathname, exactly as passed to the [*realpath*(3)](/realpath/3.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.

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

`char *result = realpath(pathname, resolved_pathname);`\
 `if (!result)`

```
{
```

`fprintf(stderr, "%s\n", explain_realpath(pathname, resolved_pathname));`

```
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_realpath\_or\_die*(3)](/explain_realpath_or_die/3.md) function.

### explain\_errno\_realpath

const char \*explain\_errno\_realpath(int errnum, const char \*pathname, char \*resolved\_pathname);

The **explain\_errno\_realpath** function is used to obtain an explanation of an error returned by the [*realpath*(3)](/realpath/3.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.

- *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*.

- *pathname*

  The original pathname, exactly as passed to the [*realpath*(3)](/realpath/3.md) system call.

- *resolved\_pathname*

  The original resolved\_pathname, exactly as passed to the [*realpath*(3)](/realpath/3.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.

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

`char *result = realpath(pathname, resolved_pathname);`\
 `if (!result)`

```
{
    int err = errno;
```

`fprintf(stderr, "%s\n", explain_errno_realpath(err, pathname,` `resolved_pathname));`

```
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_realpath\_or\_die*(3)](/explain_realpath_or_die/3.md) function.

### explain\_message\_realpath

void explain\_message\_realpath(char \*message, int message\_size, const char \*pathname, char \*resolved\_pathname);

The **explain\_message\_realpath** function is used to obtain an explanation of an error returned by the [*realpath*(3)](/realpath/3.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.

- *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.

- *pathname*

  The original pathname, exactly as passed to the [*realpath*(3)](/realpath/3.md) system call.

- *resolved\_pathname*

  The original resolved\_pathname, exactly as passed to the [*realpath*(3)](/realpath/3.md) system call.

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

`char *result = realpath(pathname, resolved_pathname);`\
 `if (!result)`

```
{
    char message[3000];
```

`explain_message_realpath(message, sizeof(message), pathname,` `resolved_pathname);`

```
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_realpath\_or\_die*(3)](/explain_realpath_or_die/3.md) function.

### explain\_message\_errno\_realpath

void explain\_message\_errno\_realpath(char \*message, int message\_size, int errnum, const char \*pathname, char \*resolved\_pathname);

The **explain\_message\_errno\_realpath** function is used to obtain an explanation of an error returned by the [*realpath*(3)](/realpath/3.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.

- *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*.

- *pathname*

  The original pathname, exactly as passed to the [*realpath*(3)](/realpath/3.md) system call.

- *resolved\_pathname*

  The original resolved\_pathname, exactly as passed to the [*realpath*(3)](/realpath/3.md) system call.

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

`char *result = realpath(pathname, resolved_pathname);`\
 `if (!result)`

```
{
    int err = errno;
    char message[3000];
```

`explain_message_errno_realpath(message, sizeof(message), err, pathname,` `resolved_pathname);`

```
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_realpath\_or\_die*(3)](/explain_realpath_or_die/3.md) function.

## SEE ALSO

- [*realpath*(3)](/realpath/3.md)

  return the canonicalized absolute pathname

- [*explain\_realpath\_or\_die*(3)](/explain_realpath_or_die/3.md)

  return the canonicalized absolute pathname and report errors

## COPYRIGHT

libexplain version 1.4\
 Copyright (C) 2011 Peter Miller