C++ vector 作为参数传递给函数问题？

将v作为参数传递给add 实现加一，代码如下：
#include <iostream>
#include <vector>
#include <cstdlib>

using namespace std;

void add(vector<int> v);

int main() {
    vector<int> v;
    for(int i = 0; i < 15; i++)
        v.push_back(rand()%20);

    vector<int>::iterator p;
    for(p = v.begin(); p != v.end(); p++)
        cout << (*p) << ",";
    cout << endl;
   
    add(v);

    for(vector<int>::iterator p = v.begin(); p != v.end(); p++)
        cout << (*p) << ",";
    cout << endl;

    return 0;
}

void add(vector<int> & B) {
    vector<int>::iterator p;
    for(p = B.begin(); p != B.end(); p++)
       (*p) += 1;
}

编译报如下错误：
/tmp/ccQrbXVR.o: In function `main':
test1.cpp:(.text+0x11c): undefined reference to `add(std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status

请帮我看看是哪儿的问题？