GDALAttribute C++ API

GDALAttribute class

class GDALAttribute : public virtual GDALAbstractMDArray

Class modeling an attribute that has a name, a value and a type, and is typically used to describe a metadata item.

The value can be (for the HDF5 format) in the general case a multidimensional array of “any” type (in most cases, this will be a single value of string or numeric type)

This is based on the HDF5 attribute concept

Since

GDAL 3.1

Subclassed by GDALMDArrayFromRasterBand::MDIAsAttribute

Public Functions

std::vector<GUInt64> GetDimensionsSize() const

Return the size of the dimensions of the attribute.

This will be an empty array for a scalar (single value) attribute.

This is the same as the C function GDALAttributeGetDimensionsSize().

GDALRawResult ReadAsRaw() const

Return the raw value of an attribute.

This is the same as the C function GDALAttributeReadAsRaw().

const char *ReadAsString() const

Return the value of an attribute as a string.

The returned string should not be freed, and its lifetime does not excess a next call to ReadAsString() on the same object, or the deletion of the object itself.

This function will only return the first element if there are several.

This is the same as the C function GDALAttributeReadAsString()

Return

a string, or nullptr.

int ReadAsInt() const

Return the value of an attribute as a integer.

This function will only return the first element if there are several.

It can fail if its value can be converted to integer.

This is the same as the C function GDALAttributeReadAsInt()

Return

a integer, or INT_MIN in case of error.

double ReadAsDouble() const

Return the value of an attribute as a double.

This function will only return the first element if there are several.

It can fail if its value can be converted to double.

This is the same as the C function GDALAttributeReadAsInt()

Return

a double value.

CPLStringList ReadAsStringArray() const

Return the value of an attribute as an array of strings.

This is the same as the C function GDALAttributeReadAsStringArray()

std::vector<int> ReadAsIntArray() const

Return the value of an attribute as an array of integers.

This is the same as the C function GDALAttributeReadAsIntArray().

std::vector<double> ReadAsDoubleArray() const

Return the value of an attribute as an array of double.

This is the same as the C function GDALAttributeReadAsDoubleArray().

bool Write(const void *pabyValue, size_t nLen)

Write an attribute from raw values expressed in GetDataType()

The values should be provided in the type of GetDataType() and there should be exactly GetTotalElementsCount() of them. If GetDataType() is a string, each value should be a char* pointer.

This is the same as the C function GDALAttributeWriteRaw().

Return

true in case of success.

Parameters

bool Write(const char *pszValue)

Write an attribute from a string value.

Type conversion will be performed if needed. If the attribute contains multiple values, only the first one will be updated.

This is the same as the C function GDALAttributeWriteString().

Return

true in case of success.

Parameters
  • pszValue: Pointer to a string.

bool WriteInt(int nVal)

Write an attribute from a integer value.

Type conversion will be performed if needed. If the attribute contains multiple values, only the first one will be updated.

This is the same as the C function GDALAttributeWriteInt().

Return

true in case of success.

Parameters
  • nVal: Value.

bool Write(double dfVal)

Write an attribute from a double value.

Type conversion will be performed if needed. If the attribute contains multiple values, only the first one will be updated.

This is the same as the C function GDALAttributeWriteDouble().

Return

true in case of success.

Parameters
  • dfVal: Value.

bool Write(CSLConstList vals)

Write an attribute from an array of strings.

Type conversion will be performed if needed.

Exactly GetTotalElementsCount() strings must be provided

This is the same as the C function GDALAttributeWriteStringArray().

Return

true in case of success.

Parameters
  • vals: Array of strings.

bool Write(const double *vals, size_t nVals)

Write an attribute from an array of double.

Type conversion will be performed if needed.

Exactly GetTotalElementsCount() strings must be provided

This is the same as the C function GDALAttributeWriteDoubleArray()

Return

true in case of success.

Parameters

GDALIHasAttribute interface

class GDALIHasAttribute

Interface used to get a single GDALAttribute or a set of GDALAttribute.

Since

GDAL 3.1

Subclassed by GDALGroup, GDALMDArray

Public Functions

std::shared_ptr<GDALAttribute> GetAttribute(const std::string &osName) const

Return an attribute by its name.

If the attribute does not exist, nullptr should be silently returned.

Drivers known to implement it for groups and arrays: MEM, netCDF.

Note

Driver implementation: this method will fallback to GetAttributeFromAttributes() is not explicitly implemented

This is the same as the C function GDALGroupGetAttribute() or GDALMDArrayGetAttribute().

Return

the attribute, or nullptr if it does not exist or an error occured.

Parameters
  • osName: Attribute name

std::vector<std::shared_ptr<GDALAttribute>> GetAttributes(CSLConstList papszOptions = nullptr) const

Return the list of attributes contained in a GDALMDArray or GDALGroup.

If the attribute does not exist, nullptr should be silently returned.

Drivers known to implement it for groups and arrays: MEM, netCDF.

Note

Driver implementation: optionally implemented. If implemented, GetAttribute() should also be implemented.

This is the same as the C function GDALGroupGetAttributes() or GDALMDArrayGetAttributes().

Return

the attributes.

Parameters
  • papszOptions: Driver specific options determining how attributes should be retrieved. Pass nullptr for default behaviour.

std::shared_ptr<GDALAttribute> CreateAttribute(const std::string &osName, const std::vector<GUInt64> &anDimensions, const GDALExtendedDataType &oDataType, CSLConstList papszOptions = nullptr)

Create an attribute within a GDALMDArray or GDALGroup.

The attribute might not be “physically” created until a value is written into it.

Optionally implemented.

Drivers known to implement it: MEM, netCDF

This is the same as the C function GDALGroupCreateAttribute() or GDALMDArrayCreateAttribute()

Return

the new attribute, or nullptr if case of error

Parameters
  • osName: Attribute name.

  • anDimensions: List of dimension sizes, ordered from the slowest varying dimension first to the fastest varying dimension last. Empty for a scalar attribute (common case)

  • oDataType: Attribute data type.

  • papszOptions: Driver specific options determining how the attribute. should be created.