C++ to MATLAB Data Type Mapping

These tables show how MATLAB^® converts C/C++ data into equivalent MATLAB data types. MATLAB uses these mappings when creating library definition files. Use this information to help you define missing information for MATLAB signatures.

Numeric Types

Scalar Integer Types

Fixed-width integer data type mappings are independent of the platform and compiler. The mappings for non-fixed-width integer types are based on the compiler.

Fixed-Width Integer Types. For these types, specify DIRECTION as "input" and SHAPE as 1.

C Fixed-Width Scalar Integer Type	Equivalent MATLAB Type
`int8_t`	`int8`
`std::complex<int8_t>`	complex `int8`
`uint8_t`	`uint8`
`std::complex<uint8_t>`	complex `uint8`
`int16_t`	`int16`
`std::complex<int16_t>`	complex `int16`
`uint16_t`	`uint16`
`std::complex<uint16_t>`	complex `uint16`
`int32_t`	`int32`
`std::complex<int32_t>`	complex `int32`
`uint32_t`	`uint32`
`std::complex<uint32_t>`	complex `uint32`
`int64_t`	`int64`
`std::complex<int64_t>`	complex `int64`
`uint64_t`	`uint64`
`std::complex<uint64_t>`	complex `uint64`

Non-Fixed-Width Integer Types. MATLAB supports these non-fixed-width C integer types. Based on the compiler used, MATLAB maps these types to the corresponding fixed-width C types, as shown in the Fixed-Width Integer Types table.

short
short int
signed short
signed short int
unsigned short
unsigned short int
int
signed int
unsigned
unsigned int
long
signed long
signed long int
unsigned long
unsigned long int
long long

Vector Integer Types

This table shows how MATLAB data types correspond to std::vector types. By default, MATLAB represents std::vector types with the MATLAB clib.array type. For more information, see MATLAB Object for C++ Arrays.

MATLAB converts the names of fundamental C++ types to upper camel case. For complex types, MATLAB adds std.complex to the clib.array type.

For these types, specify DIRECTION as "input" and SHAPE as 1.

C++ Parameter `T` Integer Type for `std::vector<T>`	Equivalent MATLAB `clib.array` Type for Interface `lib`	Element Type
`std::vector<int8_t>`	`clib.array.lib.SignedChar`	`clib.lib.SignedChar`
`std::vector<std::complex<int8_t>>`	`clib.array.lib.std.complex.SignedChar`	`clib.lib.std.complex.SignedChar`
`std::vector<uint8_t>`	`clib.array.lib.UnsignedChar`	`clib.lib.UnsignedChar`
`std::vector<std::complex<uint8_t>>`	`clib.array.lib.std.complex.UnsignedChar`	`clib.lib.std.complex.UnsignedChar`
`std::vector<int16_t>`	`clib.array.lib.Short`	`clib.lib.Short`
`std::vector<std::complex<int16_t>>`	`clib.array.lib.std.complex.Short`	`clib.lib.std.complex.Short`
`std::vector<uint16_t>`	`clib.array.lib.UnsignedShort`	`clib.lib.UnsignedShort`
`std::vector<std::complex<uint16_t>>`	`clib.array.lib.std.complex.UnsignedShort`	`clib.lib.std.complex.UnsignedShort`
`std::vector<int32_t>`	`clib.array.lib.Int`	`clib.lib.Int`
`std::vector<std::complex<int32_t>>`	`clib.array.lib.std.complex.Int`	`clib.lib.std.complex.Int`
`std::vector<uint32_t>`	`clib.array.lib.UnsignedInt`	`clib.lib.UnsignedInt`
`std::vector<std::complex<uint32_t>>`	`clib.array.lib.std.complex.UnsignedInt`	`clib.lib.std.complex.UnsignedInt`
`std::vector<int64_t>`	`clib.array.lib.LongLong`	`clib.lib.LongLong`
`std::vector<std::complex<int64_t>>`	`clib.array.lib.std.complex.LongLong`	`clib.lib.std.complex.LongLong`
`std::vector<uint64_t>`	`clib.array.lib.UnsignedLongLong`	`clib.lib.UnsignedLongLong`
`std::vector<std::complex<uint64_t>>`	`clib.array.lib.std.complex.UnsignedLongLong`	`clib.lib.std.complex.UnsignedLongLong`

Floating Point Types

For these types, specify DIRECTION as "input" and SHAPE as 1.

C Floating Point Type	Equivalent MATLAB Type
`double`	`double`
`std::complex<double>`	complex `double`
`float`	`single`
`std::complex<float>`	complex `single`

C++ Parameter `T` Floating Point Type for `std::vector<T>`	Equivalent MATLAB `clib.array` Type for Interface `lib`	Element Type^a
`std::vector<double>`	`clib.array.lib.Double`	`clib.lib.Double`
`std::vector<std::complex<double>>`	`clib.array.lib.std.complex.Double`	`clib.lib.std.complex.Double`
`std::vector<float>`	`clib.array.lib.Float`	`clib.lib.Float`
`std::vector<std::complex<float>>`	`clib.array.lib.std.complex.Float`	`clib.lib.std.complex.Float`
^a For information about using element types, see MATLAB Object for C++ Arrays.

String and Character Types

These tables show how C++ string and char data types correspond to MATLAB data types. The data mapping depends on how the type is used in the function, as a parameter, return type, or data member (property). For example, these function definitions show different uses of type T.

void fcn(T);  // T is a parameter type (MATLAB input argument)
T fcn();      // T is a return type (MATLAB output argument)

Plain C++ Character and String Types

For these types, specify DIRECTION as "input" and SHAPE as 1.

Plain C++ Character Type	Equivalent MATLAB Type
`char`	`int8`
`signed char`	`int8`
`unsigned char`	`uint8`
`wchar_t`	`char`
`char16_t`	`char`
`char32_t`	`char`

Plain C++ String Type	Equivalent MATLAB Type
`std::string`	`string` (MATLAB converts characters to the platform default encoding for `std::string`.)
`std::wstring`	`string`
`std::u16string`	`string`
`std::u32string`	`string`

C++ `char*` and `char[]` Types

C++ Parameter Type	`MLTYPE`	`SHAPE`
`char`^a `const char`	`"int8"` `"char"` `"clib.array.lib.Char"`	Scalar value Array of scalar values
`char`^a `const char`	`"string"`	`"nullTerminated"`
`char[]` `const char[]`	`"int8"` `"char"` `"clib.array.lib.Char"`	Scalar value
`char[]` `const char[]`	`"string"`	`"nullTerminated"`
`wchar_t` `const wchar_t` `wchar_t[]` `const wchar_t[]` `char16_t` `const char16_t` `char16_t[]` `const char16_t[]` `char32_t` `const char32_t` `char32_t[]` `const char32_t[]`	`"char"`	Scalar value Array of scalar values
	`"string"`	`"nullTerminated"`
^a MATLAB sets the `DIRECTION` of `char` parameter types to `"input"`. To define a `char` argument as a string output, set `DIRECTION` to `"output"` and use the `NumElementsInBuffer` name-value argument. For an example, see the `getMessage` function in the Define String Argument table.

C++ Return Type	`MLTYPE`	`SHAPE`
`char` `const char`	`"string"` (default) To delete the character buffer, specify a deleter function using the `DeleteFcn` argument in the `defineOutput` function.	`"nullTerminated"`
`char` `const char`	`"int8"`	Scalar value Array of scalar values
`wchar_t` `const wchar_t` `wchar_t[]` `const wchar_t[]` `char16_t` `const char16_t` `char16_t[]` `const char16_t[]` `char32_t` `const char32_t` `char32_t[]` `const char32_t[]`	`"string"` (default) To delete the character buffer, specify a deleter function using the `DeleteFcn` argument in the `defineOutput` function.	`"nullTerminated"`
	`"char"`	Scalar value Array of scalar values

C++ Data Member Type	Equivalent MATLAB Type
`char*` `char[]`	`string` `clib.array.lib.Char` `int8` `char`
`wchar_t` `char16_t` `char32_t*`	`string` `char`

C++ Array of Strings

C++ Array of String Parameter Type	`MLTYPE`	`SHAPE`^a
`char` `const char` `char[]` `const char[]` `wchar_t` `const wchar_t` `wchar_t[]` `const wchar_t[]` `char16_t` `const char16_t` `char16_t[]` `const char16_t[]` `char32_t` `const char32_t` `char32_t[]` `const char32_t[]`	`"string"`	{scalar value,`"nullTerminated"`} {parameter name,`"nullTerminated"`}
^a 1D array of string. The first element is the size of array and the last element is the shape of each element.

C++ Array of String Data Member Type	Equivalent MATLAB Type
`char[]` and `const char[]` `wchar_t[]` and `const wchar_t[]` `char16_t[]` and `const char16_t[]` `char32_t[]` and `const char32_t[]`	`string`

MATLAB does not support these const and non-const C++ return types.

char** and char*[]
wchar_t** and wchar_t*[]
char16_t** and char16_t*[]
char32_t** and char32_t*[]

`std::vector<T>` String Types

For these types, specify DIRECTION as "input".

C++ `std::vector<T>` String Type	Equivalent MATLAB `clib.array` Type for Interface `lib`	Element Type^a
`std::vector<std::char>`	`clib.array.lib.std.Char`	`clib.lib.std.Char`
`std::vector<std::string>`	`clib.array.lib.std.String`	`clib.lib.std.String`
`std::vector<std::wstring>`	`clib.array.lib.std.wString`	`clib.lib.std.wString`
`std::vector<std::u16string>`	`clib.array.lib.std.u16String`	`clib.lib.std.u16String`
`std::vector<std::u32string>`	`clib.array.lib.std.u32String`	`clib.lib.std.u32String`
^a For information about using element types, see MATLAB Object for C++ Arrays.

`bool` Types

For these types, specify DIRECTION as "input" and SHAPE as 1.

`bool` Type	Equivalent MATLAB Type
`bool`	`logical`

`std::vector<T>` `bool` Type	Equivalent MATLAB `clib.array` Type for `lib`	Element Type^a
`bool`	`clib.array.lib.Bool`	`clib.lib.Bool`
^a For information about using element types, see MATLAB Object for C++ Arrays.

Static Data Members

MATLAB treats public static and public const static data members as read-only properties. You cannot update the value of a static data member. For example, build an interface lib to this header file.

class Set
{
   public:
   static int p1;
   const static int p2;
};
int Set::p1 = 5;
const int Set::p2 = 10;

The help for clib.lib.Set shows p1 and p2 as properties. To use the properties in MATLAB:

res = clib.lib.Set.p1 + clib.lib.Set.p2

res = 15

Do not update a static property by using the class name. If you do, then MATLAB creates a structure named clib. You must manually clear the clib structure before calling any functions in the interface. For example, if you try to update static property p1, then clib is a variable:

clib.lib.Set.p1 = 20

clib = 
    lib: [1×1 struct]

Clear the variable before calling any commands in clib.lib.

clear clib
clib.lib.Set.p1

ans = 5

For information about using static properties as SHAPE arguments, see Use Property or Method as SHAPE.

`const` Types

MATLAB treats an object of a C++ read-only class as a const object. The name of the object is the C++ class name, and MATLAB adds "read-only" text to the object display. For example, create a MATLAB interface to this library MyClass:

const class MyClass 
{ 
    public: 
        int val1; 
        int val2; 
}; 
 
const MyClass& func();

Call the function func in MATLAB to create a const MyClass object:

res = clib.MyClass.func()

res =  
 read-only MyClass with properties: 
  val1: 1 
  val2: 2

To check if the object is const, call clibIsReadOnly.

clibIsReadOnly(res)

ans = 
  logical   
   1

The function returns logical 1 (true) if the object is read-only. Otherwise, it returns logical 0 (false).

User-Defined Types

Class and Struct Types

This table shows how to configure a C++ parameter type T in the definition file for a MATLAB interface to library libname, where T is a class or a struct.

C++ Parameter Type	Equivalent MATLAB Type in `libname`	`DIRECTION`	`SHAPE`
`T`	`clib.libname.T`	`"input"`	1
`T*`	`clib.libname.T`	`"input"`	1
`T*`	`clib.array.libname.T`	`"input"`	1 Fixed dimensions: Enter a numerical array, such as `[5,2]`. Variable dimensions: Enter a string array of parameter names, such as `["row","col"]`.
`T[]`	`clib.array.libname.T`	`"input"`	1 Fixed dimensions Variable dimensions
`T&`	`clib.libname.T`	`"input"`	1
`T**`	`clib.libname.T`	`"output"`	1
`std::vector<T>`	`clib.array.libname.T`	`"input"`	1
`std::shared_ptr<T>`	`clib.libname.T`	`"input"`	1
`std::shared_ptr<T>&`	`clib.array.libname.T`	`"input"` `"inputoutput"`	1

This table shows how to configure a C++ return type T.

C++ Return Type	Equivalent MATLAB Type in `libname`	`SHAPE`
`T`	`clib.libname.T`	1
`T*`	`clib.libname.T`	1
`T*`	`clib.array.libname.T`	1 Fixed dimensions: Enter a numerical array, such as `[5,2]`. Variable dimensions: Enter a string array of parameter names, such as `["row","col"]`.
`T[]`	`clib.array.libname.T`	1 Fixed dimensions Variable dimensions
`T&`	`clib.libname.T`	1
`std::vector<T>`	`clib.array.libname.T`	1
`std::shared_ptr<T>`	`clib.libname.T`	1
`std::shared_ptr<T>&`	`clib.array.libname.T`	1

This table shows how to configure a C++ data member type T.

C++ Data Member Type	Equivalent MATLAB Type in `libname`	`SHAPE`
`T`	`clib.libname.T`	1
`T*`	`clib.libname.T`	1
`T*`	`clib.array.libname.T`	1 Fixed dimensions: Enter a numerical array, such as `[5,2]`. Variable dimensions: Enter a string array of parameter names, such as `["row","col"]`.
`T[]`	`clib.array.libname.T`	1 Fixed dimensions Variable dimensions
`std::vector<T>`	`clib.array.libname.T`	1
`std::shared_ptr<T>`	`clib.libname.T`	1

Enumerated Types

This table shows how to configure a C++ enum type T in the definition file for a MATLAB interface to library libname, where T is an enumerated type.

C++ Parameter Type	Equivalent MATLAB Type in `libname`	`DIRECTION`	`SHAPE`
`T`	`clib.libname.T`	`"input"`	1

C++ Return Type	Equivalent MATLAB Type in `libname`	`SHAPE`
`T`	`clib.libname.T`	1

C++ Data Member Type	Equivalent MATLAB Type in `libname`	`SHAPE`
`T`	`clib.libname.T`	1

`nullptr` Argument Types

`nullptr` Input Argument Types

MATLAB provides a clib.type.nullptr type so that you can pass NULL to a function with these C++ input argument types:

Pointers to objects. However, pointers to fundamental MATLAB array types are not supported.
shared_ptr
Arrays

The clib.type.nullptr type is supported for these MATLAB argument types:

scalar object pointers
clib arrays

`nullptr` Return Types

The C++ interface returns type-specific empty values for functions that return nullptr.

For type double, MATLAB returns [] for the value double.empty.
For all other fundamental types, MATLAB returns an MLTYPE.empty value. To determine MLTYPE, look for the C or C++ type in the tables in this topic. MLTYPE is in the Equivalent MATLAB Type column.
To test for nullptr types, call the isempty function.
For non-fundamental types, MATLAB returns a nullptr object. To test for nullptr objects, call the clibIsNull function.

`void*` Argument Types

To pass void* arguments to and from C++ functions, see Define void* and void** Arguments. MATLAB does not support void* data members.

When passing a void* input argument, MATLAB converts the underlying data to the corresponding C++ type.

Fundamental Types Mapping

C++ Type	Equivalent MATLAB `void*` Type
`int8_t*`	`int8`
`uint8_t*`	`uint8`
`int16_t*`	`int16`
`uint16_t*`	`uint16`
`int32_t*`	`int32`
`uint32_t*`	`uint32`
`int64_t*`	`int64`
`uint64_t*`	`uint64`
`float*`	`single`
`double*`	`double`
`bool*`	`logical`

clib.array Types Mapping

C++ Type	Equivalent MATLAB `clib.array` Type^a for `libname`
`char*`	`clib.array.libname.Char`
`signed char*`	`clib.array.libname.SignedChar`
`unsigned char*`	`clib.array.libname.UnsignedChar`
`short*`	`clib.array.libname.Short`
`unsigned short*`	`clib.array.libname.UnsignedShort`
`int*`	`clib.array.libname.Int`
`unsigned int*`	`clib.array.libname.UnsignedInt`
`long*`	`clib.array.libname.Long`
`unsigned long*`	`clib.array.libname.UnsignedLong`
`long long*`	`clib.array.libname.LongLong`
`unsigned long long*`	`clib.array.libname.UnsignedLongLong`
`float*`	`clib.array.libname.Float`
`double*`	`clib.array.libname.Double`
`bool*`	`clib.array.libname.Bool`
^a MATLAB converts the names of fundamental C++ types to upper camel case.

typedef void* Mapping

C++ Type	Equivalent MATLAB Type for `libname`
`typedef void* Handle`	`clib.libname.Handle`

Unsupported Data Types

If the data type of an argument/return type in a class constructor, method, or function is one of these types, or if the library contains any unsupported language features, then the functionality is not included in the MATLAB interface to the library.

Any type with a size greater than 64 bits, for example long double
References to a pointer, for example int*&
Pointers or arrays of std::string
Pointers or references to enumerations
Vectors of pointers to class objects, for example std::vector<Myclass*>
Reference data members
void* data members
Multidimensional data member arrays
Modifying static data members
** pointers, except:
- MATLAB supports char** types.
- MATLAB supports ** pointers to custom classes used as function or method parameter types.
- MATLAB supports void** used as function or method parameter types.
Multilevel pointers, such as type***
C function pointers and std::function as function return types or data members. You also cannot pass a MATLAB function as input to C function pointers or std::function parameter.
Class templates with incomplete or no instantiations
union
Types defined in the std namespace, except these supported types:
- std::string
- std::wstring
- std::u16string
- std::u32string
- std::vector
- std::shared_ptr
- std::function
- std::complex

Messages About Unsupported Types

MATLAB reports on constructs that use unsupported types. To view these messages, use the Verbose option in the clibgen.generateLibraryDefinition or clibgen.buildInterface functions.

For example, suppose that functionName in ClassName is defined in HeaderFile.h. If an argument to functionName is of unsupported type type, then MATLAB does not add functionName to the definition file. In addition, if Verbose is true, then clibgen.generateLibraryDefinition displays this message.

Did not add member 'functionName' to class 'ClassName' at HeaderFile.h:290.
  'type' is not a supported type.