Converting code from c to c++ -

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• what c++ equivalent c's designated initializers? 4 answers

i'm trying convert code c c++ project using raspberry pi camera module , i'd analyse pictures it.

but on piece of code (somebody else created) error

231:8: error: expected primary-expression before ‘.’ token 

which line:

.max_stills_w = state->width, 

i tried find keeps giving me other errors

    video_port = camera->output[mmal_camera_video_port];     still_port = camera->output[mmal_camera_capture_port];      //  set camera configuration     {        mmal_parameter_camera_config_t cam_config =        {           { mmal_parameter_camera_config, sizeof(cam_config) },           .max_stills_w = state->width,           .max_stills_h = state->height,           .stills_yuv422 = 0,           .one_shot_stills = 0,           .max_preview_video_w = state->width,           .max_preview_video_h = state->height,           .num_preview_video_frames = 3,           .stills_capture_circular_buffer_height = 0,           .fast_preview_resume = 0,           .use_stc_timestamp = mmal_param_timestamp_mode_reset_stc        };        mmal_port_parameter_set(camera->control, &cam_config.hdr);     }     // set encode format on video  port 

the named structure member initialisation in c99 not implemented in c++. in c++ can perform member initialisation using constructor. e.g:

struct sconfig  {     int m_x ;     int m_y ;      sconfig( int x, int y ) : m_x(x),                               m_y(y)     {} } ; 

or:

struct sconfig  {     int m_x ;     int m_y ;      sconfig( int x, int y )     {         m_x = x ;         m_y = y ;     } } ; 

or combination of 2 methods. instantiate object thus:

sconfig myconfig( 10, 20 ) ; 

initialising m_x , m_y 10 , 20 respectively in example.

you can of course perform initialisation provided structures defined constructors; not bad thing - letting user arbitrarily decide members initialise not particularly safe or maintainable. can of course define multiple constructors perform different initialisations; want define default constructor example:

struct sconfig  {     int m_x ;     int m_y ;      sconfig( int x, int y ) : m_x(x),                               m_y(y)     {}      sconfig( ) : m_x(0),                  m_y(0)     {} } ; 

so in example:

sconfig myconfig ; 

is equivalent of following:

sconfig myconfig( 0, 0 ) ; sconfig myconfig = { 0, 0 } ; sconfig myconfig = {0} ;