Question

I have the following code: (please pardon the length of this code). I am trying to access elements of a vector within a vector.
table_info* get_table_info function gets the values of the table_info vector for a particular table. When I try to check the values of column_info vector, I an encountering a strange error, where the program suddenly terminates.

typedef struct _column_info {
char name[20];  // columns name
int type; // 0:INT, 1: CHAR
int size;
int offset; // start position
} column_info;

typedef struct _table_info {
char name[20];
int column_count;
char columns[100];
vector <column_info> col;   //col[0], col[1]...
char primary_key[5];
int recordsize;
int totalsize;
int records;
} table_info;

vector <table_info> v;

void create_table(char* tablename, struct columns *cc , int num_col, char* pkey) {
    char* new_columns;
new_columns = (char*)malloc(256*sizeof(char));
strcpy(new_columns,"");

int len = 0;
len = num_col;

for ( int i=0 ; i < len ; i++ )
{
    strcat(new_columns, cc[i].c_name);
    strcat(new_columns, ":");
    strcat(new_columns, cc[i].c_type);

    if ( strcmp(cc[i].c_type,"char") == 0 )
    {
        strcat(new_columns, "(");
        strcat(new_columns, cc[i].c_size);
        strcat(new_columns, ")");
        record_size = record_size + atoi(cc[i].c_size);
    }
    else
        record_size = record_size + 4;

    if( i != (len-1) )
        strcat(new_columns, ",");
}

    table_info new_table;

        strcpy(new_table.name, tablename);
        strcpy(new_table.columns, new_columns);
        strcpy(new_table.primary_key, pkey);
        new_table.recordsize = record_size;
        new_table.totalsize = 0;
        new_table.records = 0;

        v.push_back(new_table);

    column_info cols;
    int offset = 0;
    for(int x=0;x<num_col;x++)
    {
        strcpy(cols.name, cc[x].c_name);
        if ( strcmp(cc[x].c_type,"char") == 0 )
            cols.type = 1;
        else
            cols.type = 0;
        cols.size = atoi(cc[x].c_size);

        cols.offset = offset;
        offset += cols.size;

        new_table.col.push_back(cols);
    }

table_info* table_info;
    table_info = get_table_info(tablename);
    int offset2=0;
    int size2 = 0;

    for (int i = 0; i < num_col ; i++)
    {
     offset2 = table_info->col.at(i).offset; // ERROR: ABNORMAL PROGRAM TERMINATION
      printf("offset:%d\n",offset2);
      size2 = table_info->col.at(i).size;
    }
    }

table_info* get_table_info(const string& tablename)
{
printf("table info \n");
    for (int i = 0; i < (int) v.size(); i++)
     {
       if (strcmp(v.at(i).name, tablename.c_str()) == 0)
    return &v.at(i);
     }
     return NULL;
  }

Any idea why this program terminates? Please help.

Answer 1

The Problem is that this code:

v.push_back(new_table);

is called before the columns have added to the table. At this time the “col”-collection is empty. Then push_back pushes a copy of your table_info instance to the vector (of course with the empty col-vector). So if you add the columns it is not added to the instance in your vector but to the local instance instead. And since num_col is greater than zero it throws an exception if you try to access the columns on that line, since table_info is the instance which is stored in the vector (the one with the empty col):

offset2 = table_info->col.at(i).offset; // ERROR: ABNORMAL PROGRAM TERMINATION

The solution is to move the push_back code down, right before you call get_table_info (or after adding the columns, if you will):

// ... 
v.push_back(new_table);

table_info* table_info;
table_info = get_table_info(tablename);
// ...