## error error — error messages and error handling |

## Stability Level

Stable, unless otherwise indicated

## Functions

const char * | vips_error_buffer ()
void | vips_error_clear ()
void | vips_error_freeze ()
void | vips_error_thaw ()
void | vips_error ()
void | vips_verror ()
void | vips_error_system ()
void | vips_verror_system ()
void | vips_error_g ()
void | vips_g_error ()
void | vips_error_exit ()
int | vips_check_uncoded ()
int | vips_check_coding ()
int | vips_check_coding_known ()
int | vips_check_coding_noneorlabq ()
int | vips_check_coding_same ()
int | vips_check_mono ()
int | vips_check_bands ()
int | vips_check_bands_1or3 ()
int | vips_check_bands_atleast ()
int | vips_check_bands_1orn ()
int | vips_check_bands_1orn_unary ()
int | vips_check_bands_same ()
int | vips_check_bandno ()
int | vips_check_int ()
int | vips_check_uint ()
int | vips_check_uintorf ()
int | vips_check_noncomplex ()
int | vips_check_complex ()
int | vips_check_twocomponents ()
int | vips_check_format ()
int | vips_check_u8or16 ()
int | vips_check_8or16 ()
int | vips_check_u8or16orf ()
int | vips_check_format_same ()
int | vips_check_size_same ()
int | vips_check_oddsquare ()
int | vips_check_vector_length ()
int | vips_check_vector ()
int | vips_check_hist ()
int | vips_check_matrix ()
int | vips_check_separable ()
int | vips_check_precision_intfloat ()

## Includes

    #include <vips/vips.h>

## Description

VIPS maintains an error buffer (a log of localised text messages), a set of functions for adding messages, and a way to access and clear the buffer.

The error buffer is global, that is, it is shared between all threads. You can add to the buffer from any thread (there is a lock to prevent corruption), but it's sensible to only read and clear the buffer from the main thread of execution.

The general principle is: if you detect an error, log a message for the user. If a function you call detects an error, just propogate it and don't add another message.

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    IMAGE *im;

    if( !(im = vips_image_new_from_file( filename, NULL )) )
      // vips_image_new_from_file() will set a message, we don't need to
      return( -1 );

    if( vips_image_get_width( im ) < 100 ) {
      // we have detected an error, we must set a message
      vips_error( "myprogram", "%s", _( "width too small" ) );
      return( -1 );
    }

The domain argument most of these functions take is not localised and is supposed to indicate the component which failed.

libvips uses `g_warning()` and `g_info()` to send warning and information messages to the user. You can use the usual glib mechanisms to display or divert these messages. For example, info messages are hidden by default, but you can see them with:

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    $ G_MESSAGES_DEBUG=VIPS vipsthumbnail k2.jpg
    VIPS-INFO: thumbnailing k2.jpg
    VIPS-INFO: selected loader is VipsForeignLoadJpegFile
    VIPS-INFO: input size is 1450 x 2048
    VIPS-INFO: loading jpeg with factor 8 pre-shrink
    VIPS-INFO: converting to processing space srgb
    VIPS-INFO: residual reducev by 0.5
    VIPS-INFO: 13 point mask
    VIPS-INFO: using vector path
    VIPS-INFO: residual reduceh by 0.5
    VIPS-INFO: 13 point mask
    VIPS-INFO: thumbnailing k2.jpg as ./tn_k2.jpg

## Functions

### vips_error_buffer ()

    const char *
    vips_error_buffer (void);

Get a pointer to the start of the error buffer as a C string. The string is owned by the error system and must not be freed.

See also: `vips_error_clear()`.

#### Returns

the error buffer as a C string which must not be freed

### vips_error_clear ()

    void
    vips_error_clear (void);

Clear and reset the error buffer. This is typically called after presenting an error to the user.

See also: `vips_error_buffer()`.

### vips_error_freeze ()

    void
    vips_error_freeze (void);

Stop errors being logged. Use `vips_error_thaw()` to unfreeze. You can nest freeze/thaw pairs.

### vips_error_thaw ()

    void
    vips_error_thaw (void);

Reenable error logging.

### vips_error ()

    void
    vips_error (const char *domain,
                const char *fmt,
                ...);

Format the string in the style of `printf()` and append to the error buffer.

See also: `vips_error_system()`, `vips_verror()`.

#### Parameters

domain | the source of the error |
fmt | printf()-style format string for the error |
... | arguments to the format string |

### vips_verror ()

    void
    vips_verror (const char *domain,
                 const char *fmt,
                 va_list ap);

Append a message to the error buffer.

See also: `vips_error()`.

#### Parameters

domain | the source of the error |
fmt | printf()-style format string for the error |
ap | arguments to the format string |

### vips_error_system ()

    void
    vips_error_system (int err,
                       const char *domain,
                       const char *fmt,
                       ...);

Format the string in the style of `printf()` and append to the error buffer. Then create and append a localised message based on the system error code, usually the value of errno.

See also: `vips_verror_system()`.

#### Parameters

err | the system error code |
domain | the source of the error |
fmt | printf()-style format string for the error |
... | arguments to the format string |

### vips_verror_system ()

    void
    vips_verror_system (int err,
                        const char *domain,
                        const char *fmt,
                        va_list ap);

Format the string in the style of `printf()` and append to the error buffer. Then create and append a localised message based on the system error code, usually the value of errno.

See also: `vips_error_system()`.

#### Parameters

err | the system error code |
domain | the source of the error |
fmt | printf()-style format string for the error |
ap | arguments to the format string |

### vips_error_g ()

    void
    vips_error_g (GError **error);

This function sets the glib error pointer from the vips error buffer and clears it. It's handy for returning errors to glib functions from vips.

See `vips_g_error()` for the inverse operation.

See also: `g_set_error()`, `vips_g_error()`.

#### Parameters

error | glib error pointer. | [out]

### vips_g_error ()

    void
    vips_g_error (GError **error);

This function adds the `GError` to the vips error buffer and clears it. It's the opposite of `vips_error_g()`.

See also: `vips_error_g()`.

#### Parameters

error | glib error pointer |

### vips_error_exit ()

    void
    vips_error_exit (const char *fmt,
                     ...);

Sends a formatted error message to stderr, then sends the contents of the error buffer, if any, then shuts down vips and terminates the program with an error code.

`fmt` may be `NULL`, in which case only the error buffer is printed before exiting.

See also: `vips_error()`.

#### Parameters

fmt | printf()-style format string for the message |
... | arguments to the format string |

### vips_check_uncoded ()

    int
    vips_check_uncoded (const char *domain,
                        VipsImage *im);

Check that the image is not coded. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 on OK, or -1 on error.

### vips_check_coding ()

    int
    vips_check_coding (const char *domain,
                       VipsImage *im,
                       VipsCoding coding);

Check that the image has the required `coding` . If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |
coding | required coding |

#### Returns

0 on OK, or -1 on error.

### vips_check_coding_known ()

    int
    vips_check_coding_known (const char *domain,
                             VipsImage *im);

Check that the image is uncoded, LABQ coded or RAD coded. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 on OK, or -1 on error.

### vips_check_coding_noneorlabq ()

    int
    vips_check_coding_noneorlabq (const char *domain,
                                  VipsImage *im);

Check that the image is uncoded or LABQ coded. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 on OK, or -1 on error.

### vips_check_coding_same ()

    int
    vips_check_coding_same (const char *domain,
                            VipsImage *im1,
                            VipsImage *im2);

Check that the images have the same coding. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im1 | first image to check |
im2 | second image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_mono ()

    int
    vips_check_mono (const char *domain,
                     VipsImage *im);

Check that the image has exactly one band. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_bands ()

    int
    vips_check_bands (const char *domain,
                      VipsImage *im,
                      int bands);

Check that the image has `bands` bands. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |
bands | must have this many bands |

#### Returns

0 if OK, -1 otherwise.

### vips_check_bands_1or3 ()

    int
    vips_check_bands_1or3 (const char *domain,
                           VipsImage *im);

Check that the image has either one or three bands. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_bands_atleast ()

    int
    vips_check_bands_atleast (const char *domain,
                              VipsImage *im,
                              int bands);

Check that the image has at least `bands` bands. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |
bands | at least this many bands |

#### Returns

0 if OK, -1 otherwise.

### vips_check_bands_1orn ()

    int
    vips_check_bands_1orn (const char *domain,
                           VipsImage *im1,
                           VipsImage *im2);

Check that the images have the same number of bands, or that one of the images has just 1 band. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im1 | first image to check |
im2 | second image to check |

#### Returns

0 on OK, or -1 on error.

### vips_check_bands_1orn_unary ()

    int
    vips_check_bands_1orn_unary (const char *domain,
                                 VipsImage *im,
                                 int n);

Check that an image has 1 or `n` bands. Handy for unary operations, cf. `vips_check_bands_1orn()`. If not, set an error message and return non-zero.

See also: `vips_check_bands_1orn()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |
n | number of bands, or 1 |

#### Returns

0 on OK, or -1 on error.

### vips_check_bands_same ()

    int
    vips_check_bands_same (const char *domain,
                           VipsImage *im1,
                           VipsImage *im2);

Check that the images have the same number of bands. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im1 | first image to check |
im2 | second image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_bandno ()

    int
    vips_check_bandno (const char *domain,
                       VipsImage *im,
                       int bandno);

`bandno` should be a valid band number (ie. 0 to im->Bands - 1), or can be -1, meaning all bands. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |
bandno | band number |

#### Returns

0 if OK, -1 otherwise.

### vips_check_int ()

    int
    vips_check_int (const char *domain,
                    VipsImage *im);

Check that the image is in one of the integer formats. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_uint ()

    int
    vips_check_uint (const char *domain,
                     VipsImage *im);

Check that the image is in one of the unsigned integer formats. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_uintorf ()

    int
    vips_check_uintorf (const char *domain,
                        VipsImage *im);

Check that the image is unsigned int or float. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_noncomplex ()

    int
    vips_check_noncomplex (const char *domain,
                           VipsImage *im);

Check that the image is not complex. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_complex ()

    int
    vips_check_complex (const char *domain,
                        VipsImage *im);

Check that the image is complex. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_twocomponents ()

    int
    vips_check_twocomponents (const char *domain,
                              VipsImage *im);

Check that the image is has two "components", ie. is a one-band complex or a two-band non-complex. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_format ()

    int
    vips_check_format (const char *domain,
                       VipsImage *im,
                       VipsBandFormat fmt);

Check that the image has the specified format. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |
fmt | format to test for |

#### Returns

0 if OK, -1 otherwise.

### vips_check_u8or16 ()

    int
    vips_check_u8or16 (const char *domain,
                       VipsImage *im);

Check that the image is 8 or 16-bit unsigned integer. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_8or16 ()

    int
    vips_check_8or16 (const char *domain,
                      VipsImage *im);

Check that the image is 8 or 16-bit integer, signed or unsigned. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_u8or16orf ()

    int
    vips_check_u8or16orf (const char *domain,
                          VipsImage *im);

Check that the image is 8 or 16-bit unsigned integer, or float. Otherwise set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_format_same ()

    int
    vips_check_format_same (const char *domain,
                            VipsImage *im1,
                            VipsImage *im2);

Check that the images have the same format. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im1 | first image to check |
im2 | second image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_size_same ()

    int
    vips_check_size_same (const char *domain,
                          VipsImage *im1,
                          VipsImage *im2);

Check that the images have the same size. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im1 | first image to check |
im2 | second image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_oddsquare ()

    int
    vips_check_oddsquare (const char *domain,
                          VipsImage *im);

Check that the image is square and that the sides are odd. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_vector_length ()

    int
    vips_check_vector_length (const char *domain,
                              int n,
                              int len);

Check that `n` == `len` .

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
n | number of elements in vector |
len | number of elements vector should have |

#### Returns

0 if OK, -1 otherwise.

### vips_check_vector ()

    int
    vips_check_vector (const char *domain,
                       int n,
                       VipsImage *im);

Operations with a vector constant need a 1-element vector, or a vector with the same number of elements as there are bands in the image.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
n | number of elements in vector |
im | image to check against |

#### Returns

0 if OK, -1 otherwise.

### vips_check_hist ()

    int
    vips_check_hist (const char *domain,
                     VipsImage *im);

Histogram images must have width or height 1, and must not have more than 65536 elements. Return 0 if the image will pass as a histogram, or -1 and set an error message otherwise.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_matrix ()

    int
    vips_check_matrix (const char *domain,
                       VipsImage *im,
                       VipsImage **out);

Matrix images must have width and height less than 100000 and have 1 band.

Return 0 if the image will pass as a matrix, or -1 and set an error message otherwise.

`out` is set to be `im` cast to double and stored in memory. Use `VIPS_MATRIX()` to address values in `out` .

You must unref `out` when you are done with it.

See also: `VIPS_MATRIX()`, `vips_object_local()`

#### Parameters

domain | the originating domain for the error message |
im | image to check |
out | put image as in-memory doubles here. | [out]

#### Returns

0 if OK, -1 otherwise.

### vips_check_separable ()

    int
    vips_check_separable (const char *domain,
                          VipsImage *im);

Separable matrix images must have width or height 1. Return 0 if the image will pass, or -1 and set an error message otherwise.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
im | image to check |

#### Returns

0 if OK, -1 otherwise.

### vips_check_precision_intfloat ()

    int
    vips_check_precision_intfloat (const char *domain,
                                   VipsPrecision precision);

Check that `prec` image is either float or int. If not, set an error message and return non-zero.

See also: `vips_error()`.

#### Parameters

domain | the originating domain for the error message |
precision | precision to check |

#### Returns

0 on OK, or -1 on error.

## Types and Values