Some rather dated examples of Mophological operations using OpenCV. I wrote briefly about them at one point (https://bradmontgomery.net/blog/morphology-is-fun/), but I'm moving the sample code here.

dilate.cpp

//----------------------------------------
// Perform Image Dilation on input image,
// saving the result to an input image.
//
// USAGE: dilate <input_image> <output_image> [iterations]
//
// Version: 2009.01.04
//
// Copyright (c) 2009, Brad Montgomery <brad@bradmontgomery.net>
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
//----------------------------------------

#include "cv.h"
#include "highgui.h"
#include <iostream>
#include <stdlib.h>

// used for cvLoadImage()
#define CV_LOAD_IMAGE_COLOR       1
#define CV_LOAD_IMAGE_GRAYSCALE   0
#define CV_LOAD_IMAGE_UNCHANGED  -1

//#define SHOW_OUTPUT 1

using namespace std;

int main (int argc, char** argv) {

    char* input_filename;
    char* output_filename;
    IplImage* input_image;
    IplImage* output_image;
    int iterations = 1;

    #ifdef SHOW_OUTPUT
    const char* input_win = "Original Image";
    const char* output_win = "Dilated Image";
    #endif

    int key;

    if( argc == 3 ){
        input_filename = argv[1];
        output_filename = argv[2];
    }else if(argc == 4){
        input_filename = argv[1];
        output_filename = argv[2];
        iterations = atoi(argv[3]);
    }else{
        cerr << "USAGE: dilate <input_image> <output_image> [iterations=1]\n";
        exit(1);
    }

    // load the image
    input_image = cvLoadImage(input_filename, CV_LOAD_IMAGE_UNCHANGED);
    output_image = cvCloneImage(input_image);
    cout << "- Cloned input as output image\n";


    // void cvDilate( const CvArr* src, CvArr* dst, IplConvKernel* element=NULL,
    //                int iterations=1 );
    // if element=NULL, a 3x3 rectangular structuring element is used.
    cvDilate(input_image, output_image, NULL, iterations);


    #ifdef SHOW_OUTPUT
    //create windows
    if(!cvNamedWindow(input_win, CV_WINDOW_AUTOSIZE)){
        std::cout << "Could not create window";
        return -1;
    }
    if(!cvNamedWindow(output_win, CV_WINDOW_AUTOSIZE)){
        std::cout << "Could not create window";
        return -1;
    }
    // show the image in the window
    cvShowImage(input_win, input_image);
    cvShowImage(output_win, output_image);
    // Wait for a number of miliseconds,
    // 0 == infinity
    key = cvWaitKey(0);
    #endif

    // Save the Output Image
    // int cvSaveImage( const char* filename, const CvArr* image );
    cvSaveImage(output_filename, output_image);
    cout << "Image saved as " << output_filename << "\n done.\n\n";

    cvReleaseImage( &input_image );
    cvReleaseImage( &output_image );
    return 0;
}

erode.cpp

//----------------------------------------
// Perform Image Erosion on input image,
// saving the result to an input image.
//
// USAGE: erode <input_image> <output_image> [iterations]
//
// Version: 2009.01.04
//
// Copyright (c) 2009, Brad Montgomery <brad@bradmontgomery.net>
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
//----------------------------------------

#include "cv.h"
#include "highgui.h"
#include <iostream>
#include <stdlib.h>

// used for cvLoadImage()
#define CV_LOAD_IMAGE_COLOR       1
#define CV_LOAD_IMAGE_GRAYSCALE   0
#define CV_LOAD_IMAGE_UNCHANGED  -1

//#define SHOW_OUTPUT 1

using namespace std;

int main (int argc, char** argv) {

    char* input_filename;
    char* output_filename;
    IplImage* input_image;
    IplImage* output_image;
    int iterations = 1;

    #ifdef SHOW_OUTPUT
    const char* input_win = "Original Image";
    const char* output_win = "Eroded Image";
    #endif

    int key;

    if( argc == 3 ){
        input_filename = argv[1];
        output_filename = argv[2];
    }else if(argc == 4){
        input_filename = argv[1];
        output_filename = argv[2];
        iterations = atoi(argv[3]);
    }else{
        cerr << "USAGE: erode <input_image> <output_image> [iterations=1]\n";
        exit(1);
    }

    // load the image
    input_image = cvLoadImage(input_filename, CV_LOAD_IMAGE_UNCHANGED);
    output_image = cvCloneImage(input_image);
    cout << "- Cloned input as output image\n";


    // void cvErode( const CvArr* src, CvArr* dst, IplConvKernel* element=NULL,
    //                int iterations=1 );
    // if element=NULL, a 3×3 rectangular structuring element is used.
    cvErode(input_image, output_image, NULL, iterations);


    #ifdef SHOW_OUTPUT
    //create windows
    if(!cvNamedWindow(input_win, CV_WINDOW_AUTOSIZE)){
        std::cout << "Could not create window";
        return -1;
    }
    if(!cvNamedWindow(output_win, CV_WINDOW_AUTOSIZE)){
        std::cout << "Could not create window";
        return -1;
    }
    // show the image in the window
    cvShowImage(input_win, input_image);
    cvShowImage(output_win, output_image);
    // Wait for a number of miliseconds,
    // 0 == infinity
    key = cvWaitKey(0);
    #endif

    // Save the Output Image
    // int cvSaveImage( const char* filename, const CvArr* image );
    cvSaveImage(output_filename, output_image);
    cout << "Image saved as " << output_filename << "\n done.\n\n";

    cvReleaseImage( &input_image );
    cvReleaseImage( &output_image );
    return 0;
}

morphology.cpp

//----------------------------------------
// Perform Morphological Operations on an image,
// saving the result to an input image.
//
// USAGE: morphology <input_image> <output_image> [shape] [operation] [iterations]
//
// Version: 2009.01.04
//
// Copyright (c) 2009, Brad Montgomery <brad@bradmontgomery.net>
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
//----------------------------------------

#include "cv.h"
#include "highgui.h"
#include <iostream>
#include <cstdlib>
#include <cstring>

// used for cvLoadImage()
#define CV_LOAD_IMAGE_COLOR       1
#define CV_LOAD_IMAGE_GRAYSCALE   0
#define CV_LOAD_IMAGE_UNCHANGED  -1

//#define SHOW_OUTPUT 1

using namespace std;

int main (int argc, char** argv) {

    char* input_filename;
    char* output_filename;
    IplImage* input_image;
    IplImage* output_image;
    IplImage* temp_image;
    // Default parameters for Structuring Element
    int cols = 3;
    int rows = 3;
    int anchor_x = 0;
    int anchor_y = 0;
    int shape = CV_SHAPE_RECT;
    // Morphology paramters
    int operation = CV_MOP_OPEN;
    int iterations = 1;

    #ifdef SHOW_OUTPUT
    const char* input_win = "Original Image";
    const char* output_win = "Output Image";
    #endif

    int key;

    cout << "\n-----------------------------------------\n";
    if( argc == 3 ){
        input_filename = argv[1];
        output_filename = argv[2];
    }else if(argc == 6){
        input_filename = argv[1];
        output_filename = argv[2];

        cout << "Shape: '" << argv[3] << "'\n";
        if(strcmp(argv[3], "rectangle")   == 0) shape = CV_SHAPE_RECT;
        else if(strcmp(argv[3], "cross")  == 0) shape = CV_SHAPE_CROSS;
        else if(strcmp(argv[3], "ellipse")== 0) shape = CV_SHAPE_ELLIPSE;
        else shape= CV_SHAPE_RECT;

        cout << "Operation: '" << argv[4] << "'\n";
        if(strcmp(argv[4], "open")         == 0) operation = CV_MOP_OPEN;
        else if(strcmp(argv[4],"close")    == 0) operation = CV_MOP_CLOSE;
        else if(strcmp(argv[4],"gradient") == 0) operation = CV_MOP_GRADIENT;
        else if(strcmp(argv[4],"tophat")   == 0) operation = CV_MOP_TOPHAT;
        else if(strcmp(argv[4],"blackhat") == 0) operation = CV_MOP_BLACKHAT;
        else operation = CV_MOP_OPEN;

        iterations = atoi(argv[5]);
        cout << "Iterations: " << iterations << "\n";
    }else{
        cerr << "USAGE: morphology <input_image> <output_image> ";
        cerr << " [shape=rect] [operation=open] [iterations=1]\n";
        cerr << "   shape can be 'rectangle', 'cross', or 'ellipse'\n";
        cerr << "   operation can be 'open', 'close', 'gradient', 'tophat', or 'blackhat'\n";
        exit(1);
    }

    // load the image
    input_image = cvLoadImage(input_filename, CV_LOAD_IMAGE_UNCHANGED);
    output_image = cvCloneImage(input_image);
    temp_image = cvCloneImage(input_image);
    //cout << "- Cloned input as output image\n";

    // IplConvKernel*
    // cvCreateStructuringElementEx( int cols,      // number of columns
    //                               int rows,      // number of rows
    //                               int anchor_x,  // relative horizontal offset
    //                               int anchor_y,  //    "     vertical offset
    //                               int shape,     // (see below)
    //                               int* values=NULL ); // values for custom shape
    //  shape can be:
    //  CV_SHAPE_RECT, a rectangular element;
    //  CV_SHAPE_CROSS, a cross-shaped element;
    //  CV_SHAPE_ELLIPSE, an elliptic element;
    //  CV_SHAPE_CUSTOM, a user
    IplConvKernel* element = cvCreateStructuringElementEx(rows, cols, anchor_x, anchor_y,
                                                          shape, NULL);


    //void cvMorphologyEx( const CvArr* src, CvArr* dst, CvArr* temp,
    //                     IplConvKernel* element, int operation, int iterations=1 );
    //  Operation can be one of the following:
    //  CV_MOP_OPEN - opening
    //  CV_MOP_CLOSE - closing
    //  CV_MOP_GRADIENT - morphological gradient
    //  CV_MOP_TOPHAT - "top hat"
    //  CV_MOP_BLACKHAT - "black hat"
    cvMorphologyEx(input_image, output_image, temp_image, element, operation, iterations);
    cout << "Ran cvMophologyEx with 3x3 element of (shape: "<<shape<<", operation: " << operation << ")\n\n";
    // void cvReleaseStructuringElement( IplConvKernel** element );
    cvReleaseStructuringElement( &element );

    #ifdef SHOW_OUTPUT
    //create windows
    if(!cvNamedWindow(input_win, CV_WINDOW_AUTOSIZE)){
        std::cout << "Could not create window";
        return -1;
    }
    if(!cvNamedWindow(output_win, CV_WINDOW_AUTOSIZE)){
        std::cout << "Could not create window";
        return -1;
    }
    // show the image in the window
    cvShowImage(input_win, input_image);
    cvShowImage(output_win, output_image);
    // Wait for a number of miliseconds,
    // 0 == infinity
    key = cvWaitKey(0);
    #endif

    // Save the Output Image
    // int cvSaveImage( const char* filename, const CvArr* image );
    cvSaveImage(output_filename, output_image);
    cout << "Image saved as " << output_filename << "\n done.\n\n";

    cvReleaseImage( &input_image );
    cvReleaseImage( &output_image );
    return 0;
}