Fill a struct containing char** array as a member,

Question

...currently am practicing to fill a struct that contains an array(char array to store multiple elements). The scenario am trying to implement is as follows:

1. The general task is (to store student information, name as string and courses taken by the student as a list or char**)
2. student information is first loaded from file!(myfile.txt)
3. tokenize/parse student information and load to struct

The file that contains my student information is:

myfile.txt (each line contains student name and list of courses) delimited by ":"

Austin Barbra:Biology,chemistry,maths,music
Romio Chandra:Mechanics,IT,Geology,music,Astronomy
.
.

My main.c is:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define path "myfile.txt"

typedef struct student_info
{
    char *studt_name;
    char *cources_as_string;
    char **cources_as_list;
}std_info ;

std_info *myinfo; //a global var that will conatain student info
int student_count = 0,cource_count=0;
void load_file()
{
    int i,yu,index=0;
    char *line =NULL,* token = NULL;
    size_t len=0;
    FILE *fp;
    fp =fopen(path,"r");
    if(fp==NULL)
    {
        perror("FILE OPEN ERROR[IN load_file]: ");
        return;
    }
    if (( myinfo =  (struct student_info *) malloc( 2 * sizeof(myinfo) ) ) == NULL)//malloc for 2 students
    puts ("malloc fail");
    while (getline(&line, &len, fp) != -1 )
    {
        strtok(line,"\n");
        char *token;

        token = strtok(line,":");
        myinfo[index].studt_name=(char * ) malloc(200 * sizeof(char ) );
        strcpy(myinfo[index].studt_name,token);

        token = strtok(NULL, ":");
        myinfo[index].cources_as_string=(char * ) malloc(200 * sizeof(char ) );
        strcpy(myinfo[index].cources_as_string,token);
        index++;
    }
    student_count = index;
    fclose(fp);
}
char** return_cource_list(char* cources_string)
{
    char *token;
    char **cource_list = malloc (sizeof (char *) * 10);
    int index = 0;
    //course_string is delimited by ",": (eg. Biology,chemistry,maths,music). parse this and add to my char ** variable.
    token = strtok(cources_string,",");
    cource_list[0]= token;
    while (token != NULL)
    {
        cource_list[index]= token;
        token = strtok (NULL, ",");
        index++;
    }
    cource_count = index;
    return cource_list;

}
int main()
{
    int i,j;
    load_file();
    for(i=0;i<student_count;i++)
    {
        printf("============================\n");
        printf("NAME: %s >>COURCE_string: %s\n",myinfo[i].studt_name,myinfo[i].cources_as_string);
        char ip_list[200];
        char** std_cource_list = return_cource_list(myinfo[i].cources_as_string);
        for(j=0;j<cource_count;j++)
        {
            printf("\tCOURCE_list[%d]: %s\n",j,std_cource_list[j]);
            //segmentation fault exists here, to copy "std_cource_list[j]" to my struct...(need help here).
            strcpy(myinfo[i].cources_as_list[j],std_cource_list[j]);
        }
    }
}

The problem am facing is to fill the "char **cources_as_list;" member of the struct. Am getting a seg_fault from the inner for loop(iterating on j). Do i miss something in my code?

Answer 1

I fixed it quick so that it doesn't crash and output is correct, it can be better (there are leaks we can fix) but it actually prints your stuff now.

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

#define path "myfile.txt"

typedef struct student_info {
    char *studt_name;
    char *cources_as_string;
    char **cources_as_list;
} std_info;

std_info *myinfo; //a global var that will conatain student info
int student_count = 0, cource_count = 0;

void load_file() {
    int i, yu, index = 0;
    char *line = NULL, *token = NULL;
    size_t len = 0;
    FILE *fp;
    fp = fopen(path, "r");
    if (fp == NULL) {
        perror("FILE OPEN ERROR[IN load_file]: ");
        return;
    }
    if ((myinfo = (struct student_info *) malloc(2 * sizeof(*myinfo))) == NULL)//malloc for 2 students
        puts("malloc fail");
    while (getline(&line, &len, fp) != -1) {
        strtok(line, "\n");
        char *token;

        token = strtok(line, ":");
        myinfo[index].studt_name = malloc(200 * sizeof(char));
        strcpy(myinfo[index].studt_name, token);

        token = strtok(NULL, ":");
        myinfo[index].cources_as_string = malloc(200 * sizeof(char));
        strcpy(myinfo[index].cources_as_string, token);
        index++;
    }
    student_count = index;
    //fclose(fp);
}

char **return_cource_list(char *cources_string) {
    char *token;
    char **cource_list = malloc(sizeof(char *) * 10);
    int index = 0;
    //course_string is delimited by ",": (eg. Biology,chemistry,maths,music). parse this and add to my char ** variable.
    token = strtok(cources_string, ",");
    cource_list[0] = token;
    while (token != NULL) {
        cource_list[index] = strdup(token);
        token = strtok(NULL, ",");
        index++;
    }
    cource_count = index;
    return cource_list;

}

/* returns an array of char*, all of which NULL */
char **alloc_argv(unsigned rows) {
    char **matrix = malloc(rows * sizeof(char *));
    if (!matrix) abort();

    for (unsigned row = 0; row < rows; row++) {
        matrix[row] = malloc(rows * sizeof(char *));
        matrix[row] = "\0";
        if (!matrix[row]) abort();

    }
    return matrix;
}

int main() {
    int i, j;
    load_file();
    for (i = 0; i < student_count; i++) {
        printf("============================\n");
        printf("NAME: %s >>COURCE_string: %s\n", myinfo[i].studt_name, myinfo[i].cources_as_string);
        char ip_list[200];
        char **std_cource_list = return_cource_list(myinfo[i].cources_as_string);
        for (j = 0; j < cource_count; j++) {
            printf("\tCOURCE_list[%d]: %s\n", j, std_cource_list[j]);
            //segmentation fault exists here, to copy "std_cource_list[j]" to my struct...(need help here).


            myinfo[i].cources_as_list = alloc_argv(100);
            myinfo[i].cources_as_list[j] = malloc(sizeof(char **));
            strcpy(myinfo[i].cources_as_list[j], std_cource_list[j]);
        }
    }
}

Output

============================
NAME: Austin Barbra >>COURCE_string: Biology,chemistry,maths,music
    COURCE_list[0]: Biology
    COURCE_list[1]: chemistry
    COURCE_list[2]: maths
    COURCE_list[3]: music
============================
NAME: Romio Chandra >>COURCE_string: Mechanics,IT,Geology,music,Astronomy
    COURCE_list[0]: Mechanics
    COURCE_list[1]: IT
    COURCE_list[2]: Geology
    COURCE_list[3]: music
    COURCE_list[4]: Astronomy

Process finished with exit code 0