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Open NetCDF data source



ncid = opens the source for read-only access and returns a NetCDF identifier in ncid. Thesource specified can be the name of a NetCDF file or the URL of an OPeNDAP NetCDF data source.


ncid =,mode) opens source with the type of access specified by mode. Mode values are 'WRITE', 'SHARE', or 'NOWRITE'.

[actualChunksize,ncid] =,mode,chunksize) opens an existing NetCDF data source, with a specified chunksize. The chunksize parameter enables I/O performance tuning.


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Open the sample NetCDF file, with read-only access, read a variable, and then close the file. The function returns a file identifier.

ncid ='')
ncid = 65536

Read the data associated with the variable, avagadros_number, in the example file, using the netcdf.getVar function. The second input to netcdf.getVar is the variable ID, which is a zero-based index that identifies the variable. The avagadros_number variable has the index value 0.

A_number = netcdf.getVar(ncid,0)
A_number = 6.0221e+23

Close the NetCDF file.


Open an NetCDF and assign a value to a variable, and then display it.

Create NetCDF File containing a variable pi.


Open the file for writing and write the value 3.1416 to the variable pi.

ncid ='','WRITE')
ncid = 65536
varInd = 0; % index of the first variable in the file
varValue = 3.1416 ; 

Read and display the value of the variable pi from the file.

ans = 3.1416

Close the file.


Input Arguments

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Source name, specified as a character vector or string scalar containing the name of a NetCDF file or the URL of an OPeNDAP NetCDF data source.

Data Types: char | string

Access type, specified as a character vector or string scalar, or a numeric value. The mode input can one of these values.

Value Description
'WRITE'Read-write access
'SHARE'Synchronous file updates
'NOWRITE'Read-only access (Default)

You also can specify mode with a numeric value. Retrieve the numerical value for mode by using netcdf.getConstant. For example, netcdf.getConstant('WRITE') returns the numeric value for mode. Use these numeric values when you want to specify a bitwise-OR of several modes.

Data Types: char | string | double

Chunk size parameter for performance tuning, specified as an integer.

The chunksize parameter controls the space-versus-time tradeoff, memory that the function allocates in the NetCDF library versus the number of system calls. Because of internal requirements, the actual value of the chunk size used by the function can be different than the input value you specify. For the actual value used by the function, see the actualChunksize argument.

Example: 1024

Example: 8192

Data Types: double

Output Arguments

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File identifier of an open NetCDF file or OPeNDAP NetCDF data source, returned as an integer.

Data Types: double

Actual chunk size used by the function, returned as an integer.

Data Types: double


This function corresponds to the nc_open and nc__open functions in the netCDF library C API. To use this function, you should be familiar with the netCDF programming paradigm.

Introduced in R2011a