Question

I have declared an associative array and now want to print it:

#include <map>
#include <string>
#include <cstdio>

using namespace std;

int main() {
    map<string, int> m;

    m["Peter"] = 4;
    m["John"] = 3;
    m["Katie"] = 3;

    map<string, int>::iterator curr,end;

    for(curr = m.begin(), end = m.end(); curr != end; curr++) {
        printf("%s : %i\n", curr->first, curr->second);
    }
    return 0;
}

I’m getting an error from my compiler:

main.cpp: In function ‘int main()’:
main.cpp:24: warning: cannot pass objects of non-POD type ‘const struct std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ through ‘...’; call will abort at runtime

And surprise suprise – it’s true – call aborts at runtime…

But I don’t know why… What should I fix? What exactly mean “through ‘…’” ?

Answer 1

try:

    printf("%s : %i\n", curr->first.c_str(),  curr->second);

The c_str() method convert std::string to a c-style string (char*).

the ... refers to printf‘s vararg prototype:

int printf(const char *format, ...);

which won’t support passing c++ objects.

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BTW, you should use ++curr instead of curr++. This is some c++ magic that prevent duplicating a reference.