2

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)

我看不出这有什么不妥……

4

1 回答 1

2

是的，这是可怕的 COW 实现！您还可以强制使用 const （因此是非变异的）重载，如下所示：

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（如果您不想修改原始字符串类型）：

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

牛参考，因为我知道我在某处写过一些关于它的东西。

于 2012-09-26T15:10:39.637 回答