Question

我想删除FOR循环末尾的指针以避免内存泄漏。但是在FOR循环的中间，它可能会遇到条件if (i > maxHour / 2) continue;并从头开始继续。为了避免内存泄漏，我试图检查if (NULL != p) delete[] p;，但程序无法编译。我不确定这行if (NULL != p) delete[] p;

有什么问题

   int main() {

        int maxHour = 8760;
        int *p;
        for (int i = 0; i < maxHour; i++) {

            if (NULL != p) delete[] p;

            p = new int[100];

            //do some things 1

            if (i > maxHour / 2) continue;

            //do some things 2

            delete[] p;
        }

    return 0;
}

Answer 1

有几个问题。

首先，您需要将p初始化为nullptr，以便第一次迭代不会尝试访问并释放未初始化的指针。

其次，在循环结束时删除指针后，需要将其设置为nullptr，以便下一次迭代不会再尝试释放它。

最后，你需要在循环之后释放它，以防最后一次迭代点击continue语句，以便它跳过delete。

int main() {

    int maxHour = 8760;
    int *p = nullptr;
    for (int i = 0; i < maxHour; i++) {

        delete[] p;

        p = new int[100];

        //do some things 1

        if (i > maxHour / 2) continue;

        //do some things 2

        delete[] p;
        p = nullptr;
    }
    delete[] p;

    return 0;
}

您不需要if (NULL != p)，因为delete会自动检查空指针并且不执行任何操作。

另一种方法是在继续之前删除指针。但是，如果您有许多不同的代码分支包含continue，这可能不方便重复。

int main() {

    int maxHour = 8760;
    int *p;
    for (int i = 0; i < maxHour; i++) {

        p = new int[100];

        //do some things 1

        if (i > maxHour / 2) {
            delete[] p;
            continue;
        }

        //do some things 2

        delete[] p;
    }

    return 0;
}

Answer 2

对于这样的任务，智能指针#include <iostream> #include <memory> struct A { ~A() { std::cout << "A::~A()" << std::endl; } }; int main() { const size_t N = 10; for ( size_t i = 0; i < N; i++ ) { std::unique_ptr<A[]> p( new A[2] ); if ( i % 2 ) { std::cout << "\nContinue" << std::endl; continue; } std::cout << "\nIteration" << std::endl; } return 0; }是合适的。

这是一个示范程序

Iteration
A::~A()
A::~A()

Continue
A::~A()
A::~A()

Iteration
A::~A()
A::~A()

Continue
A::~A()
A::~A()

Iteration
A::~A()
A::~A()

Continue
A::~A()
A::~A()

Iteration
A::~A()
A::~A()

Continue
A::~A()
A::~A()

Iteration
A::~A()
A::~A()

Continue
A::~A()
A::~A()

程序输出

df<- structure(list(Pama1 = structure(c(2L, 5L, 3L, 5L, 3L, 3L, 3L, 
3L, 3L, 4L, 1L), .Label = c("", "DD1", "n/a", "PAMANA", "zf"), class = "factor"), 
    X = structure(c(11L, 3L, 10L, 2L, 4L, 5L, 6L, 7L, 8L, 9L, 
    1L), .Label = c("", "116", "12", "138", "197", "219", "224", 
    "230", "280", "85", "Start1"), class = "factor"), X.1 = structure(c(11L, 
    10L, 2L, 4L, 3L, 5L, 8L, 6L, 7L, 9L, 1L), .Label = c("", 
    "101", "145", "199", "222", "227", "233", "238", "331", "89", 
    "End1"), class = "factor"), Pama2 = structure(c(2L, 4L, 4L, 
    4L, 3L, 4L, 4L, 6L, 5L, 1L, 1L), .Label = c("", "DD2", "GGTR", 
    "n/a", "PAMANA", "T_reg"), class = "factor"), X.2 = structure(c(9L, 
    2L, 2L, 8L, 3L, 4L, 5L, 6L, 7L, 1L, 1L), .Label = c("", "1", 
    "115", "208", "214", "232", "376", "85", "Start2"), class = "factor"), 
    X.3 = structure(c(10L, 8L, 2L, 9L, 3L, 4L, 5L, 6L, 7L, 1L, 
    1L), .Label = c("", "15", "195", "229", "231", "362", "577", 
    "76", "86", "End2"), class = "factor"), Pama3 = structure(c(1L, 
    3L, 3L, 3L, 2L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("DD3", 
    "GGTR", "n/a"), class = "factor"), X.4 = structure(c(10L, 
    1L, 7L, 8L, 9L, 9L, 2L, 3L, 4L, 5L, 6L), .Label = c("1", 
    "129", "136", "153", "166", "178", "48", "65", "66", "Start1"
    ), class = "factor"), X.5 = structure(c(10L, 6L, 7L, 8L, 
    3L, 9L, 1L, 2L, 4L, 4L, 5L), .Label = c("131", "138", "144", 
    "168", "180", "34", "51", "70", "79", "End2"), class = "factor")), .Names = c("Pama1", 
"X", "X.1", "Pama2", "X.2", "X.3", "Pama3", "X.4", "X.5"), class = "data.frame", row.names = c(NA, 
-11L))

正如所见，内存被正确删除，与是否执行了continue语句无关。

您可以像使用数组一样使用带有此智能指针的下标运算符。

删除指针内存分配以避免内存泄漏

2 个答案: