c++ - 奇怪的一段代码

Question

我写了这段奇怪的代码。 type 怎么可能在它的 2 个 printf 之间改变？？

提前致谢

int main()
{
    string label = string("faults_team_A_player_12");

    size_t f = label.find('_');

    const char *type = label.substr(0,f).c_str();
    const char team = label.at(f+sizeof("team_"));

    printf("type = %s\n",type);

    int n;
    size_t l = label.length()-label.find_last_of('_');

    int x = sscanf((char *)label.substr(label.find_last_of('_'),l).c_str(),"_%d",&n);
    printf("type = %s\n",type);
    printf("team = %c\n",team);
    printf("player = %d\n",n);

    return 0;
}

输出:

type = faults
type = _12
team = A
player = 12

Answer 1

type 是 dangling pointer因为它被初始化为临时 std::string 实例的内部成员:

const char *type = label.substr(0,f).c_str();

从中获取c_str()结果的std::string实例被立即销毁。