Struct in Struct with vectors Segmentation Fault

Question

I have two structs ITEM and TABLE, one of which contains the other one, i.e. TABLE contains many ITEMS. I use this code to create the structs and the table and items with it.

#include <iostream>
#include <string>
#include <sstream>
#include <vector>

struct ITEM {
 std::string itemTitle;
};

struct TABLE {
 std::string tableName;
 int num;
 ITEM* items;
};

TABLE setTABLE(std::string, int num) {
 struct ITEM* item = (struct ITEM*) malloc(sizeof(struct ITEM) * num);
 TABLE table = {tableName, num, item};
 return table;
}

int main() {
 std::vector<TABLE> tables;
 tables.push_back(setTABLE("TEST", 3));
 tables[0].items[0].itemTitle = "TestItem";
 std::cout << tables[0].items[0].itemTitle << "\n";

 return 0;
}

I want to set the itemTitle of the ITEM at position 0, but when I cout the result i get

Segmentation fault: 11

I guess the malloc is not sufficient to this? Or is my code construction misconstrued in the first place? What I wanted to achieve is build a custom table structure.

hmjd · Accepted Answer · 2013-05-18 09:12:24Z

2

malloc() allocates memory, whereas new allocates memory and initializes (invoking a constructor of an object for example). As malloc() is being used items is a pointer to allocated but uninitialized memory which is accessed at:

tables[0].items[0].itemTitle = "TestItem";

causing the segmentation fault. But, don't use new just use a std::vector<ITEM> instead. An initial size is not required but can be supplied if required and the vector constructed with n default elements:

struct Table
{
    Table(std::string const& aName, const size_t a_num) :
        tableName(aName), items(a_num) {}
    std::string tableName;
    std::vector<Item> items;
};

Note num no longer required as items.size() can be used and don't use all uppercase as these are generally used for macros.

edited May 18, 2013 at 9:12

answered May 18, 2013 at 9:06

hmjd

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Comments

Edward Clements · Accepted Answer · 2013-05-18 09:00:48Z

0

you are returning variable table which is created on the stack -- you will need to malloc memory for table first

answered May 18, 2013 at 9:00

Edward Clements

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