mxSetFieldByNumber (MATLAB Application Program Interface)

Set a field value in a structure array, given a field number and an index

C Syntax

#include "matrix.h"
void mxSetFieldByNumber(mxArray *array_ptr, int index, 
  int field_number, mxArray *value);

Arguments

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

index
The desired element. The first element of an mxArray has an index of 0, the second element has an index of 1, and the last element has an index of N-1, where N is the total number of elements in the structure mxArray. See mxCalcSingleSubscript for details on calculating an index.

field_number
The position of the field whose value you want to extract. The first field within each element has a field_number of 0, the second field has a field_number of 1, and so on. The last field has a field_number of N-1, where N is the number of fields.

value
The value you are assigning.

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 will cause unpredictable results.

Description

Use mxSetFieldByNumber to assign a value to the specified element of the specified field. mxSetFieldByNumber is almost identical to mxSetField; however, the former takes a field number as its third argument and the latter takes a field name as its third argument.

Calling

mxSetField(pa, index, "field_name", new_value_pa);

is equivalent to calling

field_num = mxGetFieldNumber(pa, "field_name");
mxSetFieldByNumber(pa, index, field_num, new_value_pa);

Examples

See mxcreatestructarray.c in the mx subdirectory of the examples directory. For an additional example, see phonebook.c in the refbook subdirectory of the examples directory.