mxSetField (External Interfaces/API Reference)

Set a field value of a structure array, given a field name and an index

Fortran Syntax

subroutine mxSetField(pm, index, fieldname, value)
integer*4 pm, index, value
character*(*) fieldname

Arguments

pm
Pointer to a structure mxArray. Call mxIsStruct to determine if pm points to a structure mxArray.

index
The desired element. The first element of an mxArray has an index of 1, the second element has an index of 2, and the last element has an index of N, where N is the total number of elements in the structure mxArray.

fieldname
The name of the field whose value you are assigning. Call mxGetFieldNameByNumber to determine existing field names.

value
Pointer to the mxArray you are assigning. Use one of the mxCreate* functions to create the value mxArray.

Note Inputs to a MEX-file are constant read-only mxArrays and should not be modified. Using mxSetCell* or mxSetField* to modify the cells or fields of an argument passed from MATLAB causes unpredictable results.

Description

Use mxSetField to assign a value to the specified element of the specified field. If there is already a value at the given position, the value pointer you specified overwrites the old value pointer. However, mxSetField does not free the dynamic memory that the old value pointer pointed to. Consequently, you are responsible for destroying this mxArray.

mxSetField is almost identical to mxSetFieldByNumber; however, the former takes a field name as its third argument, and the latter takes a field number as its third argument.

Calling

mxSetField(pm, index, 'fieldname', newvalue)

is equivalent to calling

fieldnum = mxGetFieldNumber(pm, 'fieldname')
mxSetFieldByNumber(pm, index, fieldnum, newvalue)

mxSetDimensions mxSetFieldByNumber