c++ - Valgrind——可能丢失警告

Question

我有以下代码:

std::string myName = "BLABLABLA";

//check if there are illegal characters
for (unsigned int i = 0; i < myName.length(); i++)
{
    const char& c = myName[i];
    if (!(isalnum(c) || (c == '_') || (c == '-')))
    {
        return 0;
    }      

}

这是 valgrind 在“const char& c = myName[i];”行的输出

==17249== 51 bytes in 1 blocks are possibly lost in loss record 116 of 224
==17249==    at 0x4C2714E: operator new(unsigned long) (vg_replace_malloc.c:261)
==17249==    by 0x602A498: std::string::_Rep::_S_create(unsigned long, unsigned long,       
std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.16)
==17249==    by 0x602A689: std::string::_M_mutate(unsigned long, unsigned long,   
unsigned long) (in /usr/lib64/libstdc++.so.6.0.16)
==17249==    by 0x602AFB5: std::string::_M_leak_hard() (in 
/usr/lib64/libstdc++.so.6.0.16)
==17249==    by 0x602B0A4: std::string::operator[](unsigned long) (in /
/usr/lib64/libstdc++.so.6.0.16)

我看不出有什么不对...

Answer 1

是的，这是可怕的 COW 实现!您还可以像这样强制使用 const(因此是非变异的)重载:

std::string const myName = "BLABLABLA";

//check if there are illegal characters
for (unsigned int i = 0; i < myName.length(); i++)
{
    const char& c = myName[i];
    if (!(isalnum(c) || (c == '_') || (c == '-')))
    {
        return 0;
    }      
}

或者(如果不想修改原来的字符串类型):

std::string myName = "BLABLABLA";
std::string const &cref = myName;
//check if there are illegal characters
for (unsigned int i = 0; i < myName.length(); i++)
{
    const char& c = cref[i];
    if (!(isalnum(c) || (c == '_') || (c == '-')))
    {
        return 0;
    }      
}

等等

---

COW reference ，因为我知道我已经在某个地方写了一些关于它的东西。