e**t
发帖数: 83 | 1 今天看到Accelerated C++里的一小段程序，有困惑
// separate passing and failing student records: first try
vector extract_fails(vector& students)
{
vector pass, fail;
for (vector::size_type i = 0;
i != students.size(); ++i)
if (fgrade(students[i]))
fail.push_back(students[i]);
else
pass.push_back(students[i]);
students = pass; // 我的疑问在这里
return fail;
}
vector pass是创建在stack里，应该在function结束就被destroy |
S*****n
发帖数: 227 | 2
assignment operator语义上做的是赋值，pass destroyed了，students正好
有了新内容啊。。
【在 e**t 的大作中提到】
: 今天看到Accelerated C++里的一小段程序，有困惑
: // separate passing and failing student records: first try
: vector extract_fails(vector& students)
: {
: vector pass, fail;
: for (vector::size_type i = 0;
: i != students.size(); ++i)
: if (fgrade(students[i]))
: fail.push_back(students[i]);
: else
|
D*******a
发帖数: 3688 | 3 students是reference而不是指针
students.operator=(pass)已经把内容复制到students了
【在 e**t 的大作中提到】
: 今天看到Accelerated C++里的一小段程序，有困惑
: // separate passing and failing student records: first try
: vector extract_fails(vector& students)
: {
: vector pass, fail;
: for (vector::size_type i = 0;
: i != students.size(); ++i)
: if (fgrade(students[i]))
: fail.push_back(students[i]);
: else
|
k****z
发帖数: 550 | 4 before the function returns, the line "students = pass;" copies everything
in pass vector to the students vector, which is a reference so that the
original argument gets overwritten.
【在 e**t 的大作中提到】
: 今天看到Accelerated C++里的一小段程序，有困惑
: // separate passing and failing student records: first try
: vector extract_fails(vector& students)
: {
: vector pass, fail;
: for (vector::size_type i = 0;
: i != students.size(); ++i)
: if (fgrade(students[i]))
: fail.push_back(students[i]);
: else
|
d*******n
发帖数: 1339 | 5 students = pass; // this is a copy in vector, not a reference
【在 e**t 的大作中提到】
: 今天看到Accelerated C++里的一小段程序，有困惑
: // separate passing and failing student records: first try
: vector extract_fails(vector& students)
: {
: vector pass, fail;
: for (vector::size_type i = 0;
: i != students.size(); ++i)
: if (fgrade(students[i]))
: fail.push_back(students[i]);
: else
|
i*c
发帖数: 1132 | 6 pass在最后一个 "}" 前还没有被destroied， copy to student是有效的.
【在 e**t 的大作中提到】
: 今天看到Accelerated C++里的一小段程序，有困惑
: // separate passing and failing student records: first try
: vector extract_fails(vector& students)
: {
: vector pass, fail;
: for (vector::size_type i = 0;
: i != students.size(); ++i)
: if (fgrade(students[i]))
: fail.push_back(students[i]);
: else
|
