mxGetFieldNumber (External Interfaces/API Reference)

Get a field number, given a field name in a structure array

C Syntax

#include "matrix.h"
int mxGetFieldNumber(const mxArray *array_ptr, 
    const char *field_name);

Arguments

array_ptr
Pointer to a structure mxArray.

field_name
The name of a field in the structure mxArray.

Returns

The field number of the specified field_name, on success. The first field has a field number of 0, the second field has a field number of 1, and so on. Returns -1 on failure. Common causes of failure include:

Specifying an array_ptr that does not point to a structure mxArray. Call mxIsStruct to determine if array_ptr points to a structure mxArray.

Specifying the field_name of a nonexistent field.

Description

If you know the name of a field but do not know its field number, call mxGetFieldNumber. Conversely, if you know the field number but do not know its field name, call mxGetFieldNameByNumber.

For example, consider a MATLAB structure initialized to

patient.name = 'John Doe';
patient.billing = 127.00;
patient.test = [79 75 73; 180 178 177.5; 220 210 205];

The field_name "name" has a field number of 0; the field_name "billing" has a field_number of 1; and the field_name "test" has a field number of 2. If you call mxGetFieldNumber and specify a field_name of anything other than "name", "billing", or "test", then mxGetFieldNumber returns -1.

Calling

```
mxGetField(pa, index, "field_name");
```

is equivalent to calling

field_num = mxGetFieldNumber(pa, "field_name");
mxGetFieldByNumber(pa, index, field_num);

where index is zero if you have a one-by-one structure.

Examples

See mxcreatestructarray.c in the mx subdirectory of the examples directory.

mxGetFieldNameByNumber mxGetImagData