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Routines to load data (imporved API and Regex in C example (3)
Memory Management example from a Well House Consultants training course
More on Memory Management [link]

This example is described in the following article(s):
   • Regression testing - via a very short C testing framework - [link]
   • Encapsulating logic in functions and structs - the C approach to Object Oriented techniques - [link]

Source code: access_checkpoint_03.c Module: C212
/* Routines to load data into array of structures and access it

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <regex.h>

/* ----------- Header file ;-) ------------ */

typedef struct {
        int status;
        char *url;
        } *visit, visitData;

int loadVisits(visit **,char *);
int countVisits(char *, visit *);

#define MAXLINELENGTH 2049
#define MAXMATCHES 20

/* ----------- Internals ------------------ */

int loadVisits(visit ** incomingvisit,char * source) {
        FILE * input;
        char line[MAXLINELENGTH];
        int count=0;

        visit * sample ;

        input = fopen(source, "r");
        if (input == NULL) {
                *incomingvisit = NULL;
                return 0;

        /* Set up with TWO records initially / first will be used as a header. Naughty but nice */

        sample = NULL;
        while ((fgets(line,MAXLINELENGTH-1,input)) != NULL) {
                sample = (visit *)realloc(sample,(count+1)*sizeof(visit)); /* 4 bytes for pointer */
                sample[count] = (visitData *)malloc(sizeof(visitData)); /* The visit object itself */
                sample[count]->status = 200;
        if (count%2) sample[count]->status = 404; /* for test - alternate status 404 */
                sample[count]->url = (char *)malloc(sizeof(char) * (strlen(line)+1)); /* String for visit record */

        sample[0] = (visitData *)malloc(sizeof(visitData));
        sample[0]->status = count; /* the "naughty" bit */

        *incomingvisit = sample;

        return 1;


int countVisits(char * lookFor, visit * sample) {
        int counter;
        int k;
        visit current;
        int sampleSize;

        regex_t searchPattern;
        regmatch_t matches[MAXMATCHES];

        sampleSize = (**sample).status ;

        if (lookFor == NULL) {

                counter = sampleSize;

        } else {
                counter = 0;
                regcomp(&searchPattern,lookFor,REG_EXTENDED); /* Compile up the regular expression */
/* Should check that regex compiled properly */

                for (k=1; k<=sampleSize; k++) {
                        current = *(sample+k);
/* Exact string match equivalent of regex */
                        // if (strstr((*current).url,lookFor) != NULL) counter++;
/* Normally, regexec() returns 0 for success and the non-zero code REG_NOMATCH for failure. */
                        if (! regexec(&searchPattern,(*current).url,MAXMATCHES,matches,0)) {

        return counter;

/* ----------- Test program --------------- */

int test_03(int argc, char ** argv) {

        visit * today ;
        int nVisits;
        int matched;

        printf("Testing / running program %s\n",*argv);

        /* open and read file via a factory */
        if (loadVisits(&today,"ac_20160128")) {

                /* count up accesses to the home page */
                // matched = countVisits("/index\.html",today);

                /* Now with a regular expression */
                matched = countVisits("[[:space:]]/index\\.html",today);

                /* count up total accesses */
                nVisits = countVisits(NULL,today);

                printf("Matched %d of %d\n",matched,nVisits);

                return 0;
        } else {

                fprintf(stderr,"Input file not avaulable\n");
                return 1;
Learn about this subject
This module and example are covered on the following public courses:
 * Learning to Program in C
 * Learning to program in C and C++
 * Programming in C
 * C and C++ Programming
 * Learning to program in C and C++
 * C and C++ Programming
Also available on on site courses for larger groups

Books covering this topic
Yes. We have over 700 books in our library. Books covering C and C++ are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

Other Examples
This example comes from our "Memory Management" training module. You'll find a description of the topic and some other closely related examples on the "Memory Management" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
• Our Solutions centre provides a number of longer technical articles.
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The Horse's mouth provides a daily tip or thought.
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