Question

我试图在Node结构中初始化一个元素，但是每当我尝试访问它时，我都会遇到分段错误。我已经在Stack类中初始化了Node，但是无法在其上插入元素。

Stack.h

#ifndef QUEUE_H
#define QUEUE_H

struct Node;

// Pilha de números inteiros.
class Stack {
public:
    // Representa uma exceção que ocorre quando a pilha está vazia.
    class EmptyException {};

    // Constrói uma pilha vazia.
    Stack();

    // Insere um elemento no topo da pilha.
    void push(unsigned elem);

    // Retorna o elemento no topo da pilha.
    // Lança EmptyException caso a pilha esteja vazia.
    unsigned top() const;

    // Remove o elemento no topo da pilha.
    // Lança EmptyException caso a pilha esteja vazia.
    void pop();

    // Retorna o número de elementos na pilha.
    unsigned count() const;
private:
    Node* _top{};
    unsigned _count;
};

#endif

Stack.cpp-分段错误发生在第10行

#include "Stack.h"

struct Node {
    unsigned elem{};
    Node * next{};
};

Stack::Stack() {
    this->_count = 0;
    this->_top->elem = 0; // This is where the segmentation fault is occurring
}

void Stack::push(unsigned elem) {
    this->_top->elem = elem;
    this->_count++;
}

void Stack::pop() {
    // TODO.
}

unsigned Stack::top() const {
    return 0;
}

unsigned Stack::count() const {
    return 0;  // TODO.
}

Answer 1

在您的Stack类的构造函数中，在初始化任何有意义的东西之前，您正在使用（取消引用）top_成员指针。由于它的值可能是某种垃圾，因此您尝试访问未为您的进程设置的虚拟内存段中的地址。这样就会出现“分段错误”。

如何避免这种情况？

在启用警告的情况下编译代码。然后，编译器会告诉您有关未初始化值的使用。
有关为何应启用警告的更多信息，请阅读以下SO问题：
Why should I always enable compiler warnings?
最好在初始化列表中按顺序初始化类的成员。
有关为何应使用初始化列表的讨论，请阅读以下SO问题：
Why should I prefer to use member initialization lists?
在您的特定类中-当堆栈的顶部元素不存在时，请不要尝试为其设置值。即top_的正确初始化是对nullptr的尝试-尝试取消引用它仍然会崩溃。

您可能还需要考虑（这些不是建议，只是想法）：

使用std::unique_ptr代替原始指针。这将为您提供异常而不是硬崩溃，再加上您绝不会错误地泄漏内存。
为堆栈使用非列表式结构（例如，更像是std :: vector）。由于除了弹出之外，您不对堆栈的内容进行任何迭代，因此您不必担心重新分配后迭代器会失效。
使用std::stack（除非这是编程练习，在这种情况下不要紧）。

Answer 2

通过使用myData <- structure(list(V1 = structure(c(17L, 18L, 2L, 2L, 2L, 11L, 11L, 11L, 11L, 1L, 14L, 1L, 1L, 16L, 18L, 2L, 2L, 2L, 12L, 12L, 12L, 12L, 1L, 15L, 18L, 2L, 2L, 11L, 11L, 1L, 13L), .Label = c("", "1999", "1999Dec", "1999Nov", "1999Q3", "2000", "2000Dec", "2000Nov", "2000Q3", "2003", "2003Dec", "2003Q4", "ASSUMPTIONS", "CORE INFLATION EXPECTATIONS; YEAR-ON-YEAR CHANGE IN CORE", "EXPECTED UNEMPLOYMENT RATE; PERCENTAGE OF LABOUR FORCE", "GROWTH EXPECTATIONS; YEAR-ON-YEAR CHANGE IN REAL GDP", "INFLATION EXPECTATIONS; YEAR-ON-YEAR CHANGE IN HICP", "TARGET_PERIOD" ), class = "factor"), V2 = structure(c(1L, 68L, 2L, 10L, 17L, 64L, 65L, 66L, 67L, 1L, 1L, 1L, 1L, 1L, 68L, 2L, 10L, 17L, 64L, 65L, 66L, 67L, 1L, 1L, 68L, 2L, 10L, 66L, 67L, 1L, 1L), .Label = c("", "1", "10", "11", "14", "16", "17", "18", "19", "2", "20", "23", "24", "26", "28", "29", "3", "31", "32", "33", "34", "35", "36", "37", "38", "39", "4", "40", "43", "45", "46", "47", "5", "50", "52", "53", "54", "55", "56", "59", "6", "60", "61", "62", "63", "64", "65", "67", "68", "7", "70", "71", "72", "73", "76", "85", "86", "87", "88", "89", "9", "90", "91", "92", "93", "94", "95", "FCT_SOURCE"), class = "factor"), V3 = structure(c(1L, 96L, 16L, 16L, 13L, 62L, 1L, 28L, 23L, 1L, 1L, 1L, 1L, 1L, 96L, 55L, 59L, 28L, 55L, 1L, 67L, 67L, 1L, 1L, 96L, 31L, 29L, 34L, 91L, 1L, 1L), .Label = c("", ".25", ".28", ".3", ".4", ".5", ".53", ".6", ".64", ".68", ".7", ".71", ".8", ".9", ".97", "1", "1.1", "1.2", "1.3", "1.33", "1.38", "1.4", "1.5", "1.53", "1.6", "1.7", "1.8", "1.9", "10", "10.1", "10.2", "10.3", "10.4", "10.5", "10.6", "10.7", "10.73", "10.78", "10.8", "10.9", "11", "11.02", "11.1", "11.16", "11.2", "11.22", "11.24", "11.3", "11.4", "11.5", "11.6", "11.7", "11.9", "12", "2", "2.02", "2.04", "2.1", "2.2", "2.25", "2.26", "2.3", "2.31", "2.36", "2.37", "2.4", "2.5", "2.6", "2.7", "2.75", "2.8", "2.9", "3", "3.1", "3.2", "7.7", "7.8", "8", "8.1", "8.3", "8.5", "8.6", "8.75", "8.8", "9", "9.2", "9.3", "9.39", "9.4", "9.43", "9.5", "9.6", "9.7", "9.8", "9.9", "POINT"), class = "factor"), V4 = structure(c(1L, 57L, 1L, 1L, 1L, 1L, 1L, 1L, 43L, 1L, 1L, 1L, 1L, 1L, 57L, 1L, 1L, 1L, 1L, 1L, 1L, 29L, 1L, 1L, 58L, 1L, 1L, 1L, 32L, 1L, 1L), .Label = c("", ".1001001", ".2004008", ".29910269", ".69375619", ".7", ".999001", "0", "1", "1.01010101", "1.1", "1.18694362", "1.2", "1.3986014", "1.49700599", "1.6", "1.98019802", "1.998002", "10", "11", "11.11111111", "15", "16", "17", "19", "2", "2.02020202", "2.3", "2.97029703", "20", "21", "26", "3", "3.5", "3.5892323", "3.96039604", "30", "37", "37.9", "4", "4.54545455", "4.60921844", "4.95049505", "40", "5", "5.05050505", "5.08982036", "5.09490509", "5.5", "50", "6", "60", "70", "8", "9", "9.8", "T0_0", "T9_0" ), class = "factor"), V5 = structure(c(1L, 86L, 1L, 11L, 28L, 1L, 1L, 1L, 84L, 1L, 1L, 1L, 1L, 1L, 86L, 1L, 1L, 1L, 1L, 1L, 1L, 54L, 1L, 1L, 87L, 1L, 1L, 11L, 33L, 1L, 1L), .Label = c("", ".5", ".6006006", ".82378943", ".99009901", "0", "1", "1.01010101", "1.2012012", "1.29611167", "10", "10.37067461", "11", "12", "13", "14", "15", "17", "18.28171828", "18.8", "19", "2", "2.00400802", "2.27948464", "2.52525253", "2.8", "2.97029703", "20", "21.21212121", "22", "22.22222222", "23", "24.5", "25", "26", "26.9", "28", "29", "29.9", "3", "3.03030303", "3.26409496", "3.35353113", "3.7", "30", "34.34343434", "35", "4", "4.5", "4.60921844", "4.7", "4.76602183", "4.8951049", "4.95049505", "40", "40.59405941", "43.56435644", "45", "5", "5.26315789", "5.5", "5.55555556", "5.69430569", "5.94059406", "50", "6", "6.08175474", "6.1", "6.2", "6.41751201", "6.5277921", "6.78642715", "60", "68", "7", "7.14360752", "7.19280719", "7.92079208", "75", "8", "8.08080808", "8.4", "8.68263473", "8.91089109", "9.09090909", "F0_0T0_4", "F9_0T9_4"), class = "factor"), V6 = structure(c(1L, 103L, 41L, 61L, 81L, 1L, 1L, 1L, 26L, 1L, 1L, 1L, 1L, 1L, 103L, 1L, 1L, 1L, 1L, 1L, 1L, 73L, 1L, 1L, 104L, 5L, 74L, 8L, 49L, 1L, 1L), .Label = c("", ".5", ".5988024", ".98", "0", "1.01010101", "1.93814019", "10", "10.22044088", "11", "11.46560319", "11.47704591", "12", "12.05599666", "12.68731269", "13", "13.31830865", "13.40105912", "14", "14.1", "14.2", "14.61461461", "14.6609717", "14.8", "15", "15.84158416", "16", "16.16161616", "17", "17.08291708", "17.22870049", "17.3", "18", "18.3046303", "18.58141858", "19", "2", "2.4024024", "2.52525253", "2.97029703", "20", "21.05263158", "21.3", "22", "22.22222222", "22.9", "23", "24", "24.5", "25", "25.64870259", "26", "27.1", "28", "29", "29.29292929", "3", "3.0223655", "3.48953141", "3.76610505", "30", "32.1", "32.57007906", "33.86613387", "35", "36.36363636", "38.38383838", "39", "4", "4.45103858", "4.5", "4.70753205", "4.95049505", "40", "45", "48.51485149", "49.49494949", "5", "5.55555556", "5.94059406", "50", "51.48514851", "55", "6", "6.06060606", "60", "7", "7.29355033", "7.3", "7.51503006", "7.92079208", "70", "73", "75", "8", "8.80903491", "80", "9", "9.09090909", "9.4", "90", "95", "F0_5T0_9", "F9_5T9_9" ), class = "factor"), V7 = structure(c(1L, 112L, 102L, 95L, 66L, 1L, 1L, 35L, 36L, 1L, 1L, 1L, 1L, 1L, 112L, 1L, 1L, 1L, 1L, 1L, 1L, 7L, 1L, 1L, 113L, 72L, 95L, 66L, 8L, 1L, 1L), .Label = c("", "10", "10.2", "10.92184369", "11", "11.11111111", "11.38613861", "11.5", "12", "12.5", "12.76180698", "12.87128713", "13", "13.13131313", "13.86138614", "14", "14.64646465", "14.83150891", "15", "15.78947368", "15.84158416", "15.86826347", "16.5", "16.94915254", "17.82178218", "18", "18.18181818", "18.4", "18.5", "19", "2", "2.02020202", "2.5", "2.97029703", "20", "20.79207921", "21", "21.05263158", "21.42018153", "22.22222222", "22.4", "22.74937858", "23.17682318", "23.23232323", "23.4", "23.5", "23.87612388", "23.9134977", "24", "24.24242424", "24.27", "24.76100431", "24.8", "25", "25.8", "26", "26.26262626", "26.50190878", "26.55310621", "26.6", "27", "27.87460039", "28.2", "28.97102897", "3", "30", "30.5", "31", "31.36863137", "32", "33", "33.33333333", "34.83033932", "35", "36.36363636", "37.04692474", "4", "4.19161677", "40", "40.1", "42.5", "44.04404404", "44.44444444", "45", "45.29246795", "45.45454545", "47.36842105", "5", "5.55555556", "5.7", "50", "55", "6", "6.49728861", "60", "65", "7.50750751", "7.63131814", "7.91295747", "7.91859762", "7.92079208", "70", "75", "8.47457627", "8.6", "80", "9", "9.09090909", "9.9009901", "90", "95", "F1_0T1_4", "F10_0T10_4" ), class = "factor"), V8 = structure(c(1L, 109L, 4L, 1L, 1L, 1L, 1L, 93L, 49L, 1L, 1L, 1L, 1L, 1L, 109L, 89L, 93L, 102L, 1L, 1L, 4L, 8L, 1L, 1L, 110L, 96L, 1L, 77L, 10L, 1L, 1L), .Label = c("", ".99009901", "1.2", "10", "100", "11", "11.11111111", "11.38613861", "11.48851149", "11.5", "11.96834817", "12", "12.12121212", "12.38850347", "12.5", "12.87128713", "12.9", "13", "13.7", "14.12825651", "14.64646465", "14.93271741", "15", "15.34354221", "15.46906188", "15.55333998", "15.84158416", "15.9154325", "16", "16.01601602", "16.30390144", "16.4", "16.5", "16.78817127", "16.83168317", "17", "17.82178218", "17.96407186", "18", "18.18181818", "18.2", "18.5", "18.81188119", "19.64107677", "2", "2.5", "20", "20.1", "20.79207921", "21", "21.05263158", "21.77822178", "21.78217822", "21.9", "21.95608782", "23", "23.16070475", "23.23232323", "23.3", "23.5", "24", "24.1", "24.24242424", "24.39331863", "25", "25.5", "25.6", "26", "26.02866866", "26.46709175", "26.7", "27.27272727", "27.47252747", "29.07438362", "3", "3.03030303", "30", "30.5", "31", "31.3", "33.33333333", "33.43343343", "34.76953908", "35", "36.84210526", "38.29616235", "40", "42.5", "43", "45", "45.29246795", "5", "50", "52.63157895", "55", "55.55555556", "58.89", "6", "60", "65", "7.07070707", "70", "75", "8", "80", "9.09090909", "90", "95", "F1_5T1_9", "F10_5T10_9"), class = "factor"), V9 = structure(c(1L, 115L, 1L, 1L, 1L, 1L, 1L, 78L, 25L, 1L, 1L, 1L, 1L, 1L, 115L, 91L, 96L, 78L, 1L, 1L, 78L, 17L, 1L, 1L, 114L, 11L, 1L, 7L, 5L, 1L, 1L), .Label = c("", ".2", ".3", "0", "1", "1.01010101", "10", "10.8", "100", "11", "11.11111111", "12", "12.48751249", "13", "14", "14.8", "14.85148515", "14.9118284", "15", "15.18481518", "15.23244313", "15.3", "15.34653465", "15.48", "15.84158416", "16", "16.16161616", "16.23246493", "16.45193261", "16.46181322", "16.46276025", "16.5", "16.56686627", "17", "17.5", "17.6", "17.8", "17.84646062", "18", "18.18181818", "18.2", "18.35728953", "18.53710625", "18.68686869", "19", "19.19191919", "19.8", "2", "2.0979021", "2.2", "20", "20.07992008", "20.64128257", "20.79207921", "21", "21.03688933", "21.0958608", "21.68825742", "22.01289543", "22.05143661", "22.22222222", "22.72727273", "23.42342342", "23.49869452", "23.76237624", "24", "24.8", "25", "26.31578947", "27", "27.27272727", "27.72277228", "28", "29", "29.74051896", "3.00852244", "3.03030303", "30", "33.33333333", "33.66336634", "35", "36.36363636", "38.1", "38.88888889", "4", "4.5", "4.54545455", "4.70753205", "40", "45", "47", "47.5", "5", "5.26315789", "5.5", "50", "53.53535354", "55", "6", "6.38722555", "6.40640641", "6.5", "60", "65", "7.5", "70", "75", "8", "8.5", "80", "9", "90", "95", "F11_0T11_4", "F2_0T2_4"), class = "factor"), V10 = structure(c(1L, 95L, 1L, 1L, 1L, 1L, 1L, 1L, 89L, 1L, 1L, 1L, 1L, 1L, 95L, 11L, 1L, 1L, 1L, 1L, 72L, 20L, 1L, 1L, 94L, 1L, 1L, 11L, 9L, 1L, 1L), .Label = c("", ".1", ".1998002", ".21562789", ".3003003", ".38", ".89820359", "0", "1", "1.4", "10", "10.98772023", "11", "11.52058792", "12", "12.4750499", "12.66201396", "12.8", "13", "14.85148515", "15", "15.34653465", "15.7", "15.84158416", "16", "16.32047478", "16.4", "16.41983258", "16.5", "16.73346693", "17.5", "17.82178218", "17.839445", "18.21355236", "18.68686869", "19.19191919", "2", "2.997003", "20", "20.2020202", "21", "21.03688933", "21.05263158", "21.78217822", "23.38303445", "23.42342342", "23.76237624", "25", "25.34645511", "26.4", "27", "27.27272727", "27.77777778", "29.74051896", "3", "3.9", "30", "33", "33.33333333", "33.66336634", "35", "36.36363636", "4.2", "4.5", "40", "45", "47.5", "5", "5.0331525", "5.11022044", "5.22842116", "50", "54.54545455", "6", "6.4", "6.5", "60", "7.4", "7.5", "7.60584095", "70", "75", "8", "8.08080808", "8.09190809", "8.19180819", "8.4", "8.5", "8.91089109", "80", "9", "9.91433347", "90", "F11_5T11_9", "F2_5T2_9"), class = "factor"), V11 = structure(c(1L, 70L, 1L, 1L, 1L, 1L, 1L, 1L, 44L, 1L, 1L, 1L, 1L, 1L, 70L, 1L, 1L, 1L, 1L, 1L, 13L, 18L, 1L, 1L, 69L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("", ".0998004", ".3", ".3996004", ".5", ".501002", ".99009901", "1", "1.01010101", "1.12405899", "1.4", "1.998002", "10", "10.89108911", "11", "11.11111111", "11.2", "11.38613861", "11.88118812", "12", "12.12121212", "12.9258517", "13", "13.1", "13.13131313", "14", "14.73788328", "15", "15.46906188", "15.55333998", "15.75817641", "15.77591758", "15.84158416", "15.93429158", "16.01601602", "17", "18", "18.37598227", "18.72866037", "2", "2.02020202", "2.40571489", "2.5", "2.97029703", "20", "22.72727273", "25", "26", "3", "3.1", "3.6", "30", "4", "4.7952048", "4.81580352", "5", "5.94059406", "6", "6.56565657", "7.07070707", "7.07876371", "7.3", "7.68463074", "70", "8", "9", "9.09090909", "9.9009901", "F12_0", "F3_0T3_4"), class = "factor"), V12 = structure(c(1L, 47L, 1L, 1L, 1L, 1L, 1L, 1L, 8L, 1L, 1L, 1L, 1L, 1L, 48L, 1L, 1L, 1L, 1L, 1L, 1L, 14L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("", ".2", ".2997003", ".3", ".6", ".8", ".9", ".99009901", "1", "1.01010101", "10", "11", "11.17705242", "11.38613861", "11.39742319", "12", "13.13131313", "15", "2", "2.5", "2.97029703", "20", "3", "30", "4", "4.19161677", "4.68594217", "5", "5.25", "5.94059406", "6", "6.08782435", "6.16232465", "6.56565657", "7.07070707", "7.27623954", "7.50750751", "7.9", "7.92079208", "8", "8.47457627", "9.05804378", "9.09090909", "9.6201232", "9.9009901", "9.94358251", "F3_5", "F3_5T3_9"), class = "factor"), V13 = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 26L, 1L, 1L, 1L, 1L, 1L, 1L, 12L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("", ".3", ".5988024", ".99009901", "0", "1", "1.01010101", "1.98019802", "10", "11", "11.7938553", "11.88118812", "13.7487636", "2", "3.003003", "4.78564307", "5", "5.25", "6.16232465", "7", "7.9", "7.92079208", "8.08080808", "9", "9.09090909", "F4_0"), class = "factor")), row.names = c(1L, 2L, 3L, 4L, 5L, 395L, 396L, 397L, 398L, 399L, 400L, 401L, 402L, 403L, 404L, 405L, 406L, 407L, 797L, 798L, 799L, 800L, 801L, 802L, 803L, 804L, 805L, 1198L, 1199L, 1200L, 1201L), class = "data.frame")初始化指针来解决

尝试访问指向节点的指针时出现分段错误

2 个答案: