[1022] | 1 | /** \file |
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| 2 | Attribute functions |
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| 3 | |
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| 4 | These functions read and write attributes. |
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| 5 | |
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| 6 | Copyright 2010 University Corporation for Atmospheric |
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| 7 | Research/Unidata. See \ref copyright file for more info. */ |
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| 8 | |
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| 9 | #include "ncdispatch.h" |
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| 10 | |
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| 11 | /** \defgroup attributes Attributes |
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| 12 | |
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| 13 | Attributes hold metadata about data and files. |
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| 14 | |
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| 15 | \image html ncatts.png "Attributes store metadata." |
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| 16 | |
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| 17 | Attributes may be associated with a netCDF variable to specify such |
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| 18 | properties as units, special values, maximum and minimum valid values, |
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| 19 | scaling factors, and offsets. |
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| 20 | |
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| 21 | Attributes for a netCDF dataset are defined when the dataset is first |
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| 22 | created, while the netCDF dataset is in define mode. Additional |
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| 23 | attributes may be added later by reentering define mode. |
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| 24 | |
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| 25 | A netCDF attribute has a netCDF variable to which it is assigned, a |
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| 26 | name, a type, a length, and a sequence of one or more values. |
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| 27 | |
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| 28 | An attribute is designated by its variable ID and name. When an |
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| 29 | attribute name is not known, it may be designated by its variable ID |
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| 30 | and number in order to determine its name, using the function |
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| 31 | nc_inq_attname(). |
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| 32 | |
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| 33 | The attributes associated with a variable are typically defined |
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| 34 | immediately after the variable is created, while still in define |
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| 35 | mode. The data type, length, and value of an attribute may be changed |
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| 36 | even when in data mode, as long as the changed attribute requires no |
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| 37 | more space than the attribute as originally defined. |
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| 38 | |
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| 39 | It is also possible to have attributes that are not associated with |
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| 40 | any variable. These are called global attributes and are identified by |
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| 41 | using ::NC_GLOBAL as a variable pseudo-ID. Global attributes are usually |
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| 42 | related to the netCDF dataset as a whole and may be used for purposes |
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| 43 | such as providing a title or processing history for a netCDF dataset. |
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| 44 | |
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| 45 | Operations supported on attributes are: |
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| 46 | - Create an attribute, given its variable ID, name, data type, length, |
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| 47 | and value. |
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| 48 | - Get attribute's data type and length from its variable ID and name. |
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| 49 | - Get attribute's value from its variable ID and name. |
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| 50 | - Copy attribute from one netCDF variable to another. |
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| 51 | - Get name of attribute from its number. |
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| 52 | - Rename an attribute. |
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| 53 | - Delete an attribute. |
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| 54 | */ |
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| 55 | |
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| 56 | /*! \{*/ /* All these functions are part of the above defgroup... */ |
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| 57 | |
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| 58 | |
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| 59 | /** \name Deleting and Renaming Attributes |
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| 60 | |
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| 61 | Functions to delete or rename an attribute. */ |
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| 62 | /*! \{ */ /* All these functions are part of this named group... */ |
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| 63 | |
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| 64 | /*! |
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| 65 | Rename an attribute. |
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| 66 | |
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| 67 | The function nc_rename_att() changes the name of an attribute. If the |
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| 68 | new name is longer than the original name, the netCDF dataset must be |
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| 69 | in define mode. You cannot rename an attribute to have the same name |
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| 70 | as another attribute of the same variable. |
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| 71 | |
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| 72 | \param ncid NetCDF or group ID, from a previous call to nc_open(), |
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| 73 | nc_create(), nc_def_grp(), or associated inquiry functions such as |
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| 74 | nc_inq_ncid(). |
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| 75 | |
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| 76 | \param varid Variable ID of the attribute's variable, or ::NC_GLOBAL for |
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| 77 | a global attribute. |
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| 78 | |
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| 79 | \param name Attribute \ref object_name. |
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| 80 | |
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| 81 | \param newname The new attribute \ref object_name. |
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| 82 | |
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| 83 | <h1>Example</h1> |
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| 84 | |
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| 85 | Here is an example using nc_rename_att() to rename the variable |
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| 86 | attribute units to Units for a variable rh in an existing netCDF |
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| 87 | dataset named foo.nc: |
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| 88 | |
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| 89 | \code |
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| 90 | #include <netcdf.h> |
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| 91 | ... |
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| 92 | int status; |
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| 93 | int ncid; |
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| 94 | int rh_id; |
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| 95 | ... |
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| 96 | status = nc_open("foo.nc", NC_NOWRITE, &ncid); |
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| 97 | if (status != NC_NOERR) handle_error(status); |
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| 98 | ... |
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| 99 | status = nc_inq_varid (ncid, "rh", &rh_id); |
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| 100 | if (status != NC_NOERR) handle_error(status); |
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| 101 | ... |
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| 102 | status = nc_rename_att(ncid, rh_id, "units", "Units"); |
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| 103 | if (status != NC_NOERR) handle_error(status); |
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| 104 | \endcode |
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| 105 | */ |
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| 106 | int |
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| 107 | nc_rename_att(int ncid, int varid, const char *name, const char *newname) |
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| 108 | { |
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| 109 | NC* ncp; |
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| 110 | int stat = NC_check_id(ncid, &ncp); |
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| 111 | if(stat != NC_NOERR) return stat; |
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| 112 | return ncp->dispatch->rename_att(ncid, varid, name, newname); |
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| 113 | } |
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| 114 | |
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| 115 | /*! |
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| 116 | Delete an attribute. |
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| 117 | |
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| 118 | The function nc_del_att() deletes a netCDF attribute from an open |
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| 119 | netCDF dataset. The netCDF dataset must be in define mode. |
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| 120 | |
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| 121 | \param ncid NetCDF or group ID, from a previous call to nc_open(), |
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| 122 | nc_create(), nc_def_grp(), or associated inquiry functions such as |
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| 123 | nc_inq_ncid(). |
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| 124 | |
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| 125 | \param varid Variable ID of the attribute's variable, or ::NC_GLOBAL |
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| 126 | for a global attribute. |
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| 127 | |
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| 128 | \param name Attribute name. |
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| 129 | |
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| 130 | <h1>Example</h1> |
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| 131 | |
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| 132 | Here is an example using nc_del_att() to delete the variable attribute |
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| 133 | Units for a variable rh in an existing netCDF dataset named foo.nc: |
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| 134 | |
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| 135 | \code |
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| 136 | #include <netcdf.h> |
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| 137 | ... |
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| 138 | int status; |
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| 139 | int ncid; |
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| 140 | int rh_id; |
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| 141 | ... |
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| 142 | status = nc_open("foo.nc", NC_WRITE, &ncid); |
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| 143 | if (status != NC_NOERR) handle_error(status); |
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| 144 | ... |
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| 145 | status = nc_inq_varid (ncid, "rh", &rh_id); |
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| 146 | if (status != NC_NOERR) handle_error(status); |
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| 147 | ... |
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| 148 | status = nc_redef(ncid); |
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| 149 | if (status != NC_NOERR) handle_error(status); |
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| 150 | status = nc_del_att(ncid, rh_id, "Units"); |
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| 151 | if (status != NC_NOERR) handle_error(status); |
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| 152 | status = nc_enddef(ncid); |
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| 153 | if (status != NC_NOERR) handle_error(status); |
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| 154 | \endcode |
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| 155 | */ |
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| 156 | int |
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| 157 | nc_del_att(int ncid, int varid, const char *name) |
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| 158 | { |
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| 159 | NC* ncp; |
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| 160 | int stat = NC_check_id(ncid, &ncp); |
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| 161 | if(stat != NC_NOERR) return stat; |
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| 162 | return ncp->dispatch->del_att(ncid, varid, name); |
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| 163 | } |
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| 164 | /*! \} */ /* End of named group ...*/ |
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| 165 | |
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| 166 | /*! \} */ /* End of defgroup. */ |
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