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std",[959,1146,1113],{"class":969},[959,1148,1149],{"class":1068},"endl",[959,1151,1152],{"class":969},";\n",[959,1154,1156],{"class":961,"line":1155},11,[959,1157,1158],{"class":969},"}\n",[943,1160,1161],{"id":1161},"形成抽象类",[918,1163,1164],{},"此外，如果希望某个类成为抽象类，但没有其余合适的成为纯虚函数的成员时，可以选择将析构函数设置为纯虚的。",[950,1166,1168],{"className":952,"code":1167,"language":954,"meta":955,"style":955},"#include \u003Ciostream>\nstruct Animal {\n    virtual ~Animal() = 0; \u002F\u002F 令 Animal 为抽象类\n};\n\n\u002F\u002F 必须给出定义，原因见下\nAnimal::~Animal() { }\n\nstruct Cat : public Animal {\n    void meow() const {\n        std::cout \u003C\u003C \"meow~\" \u003C\u003C std::endl;\n    }\n};\n\nint main() {\n    \u002F\u002F Animal a;                \u002F\u002F 编译错误\n    \u002F\u002F Animal* p{new Animal{}}; \u002F\u002F 编译错误\n    Animal* q{new Cat{}};       \u002F\u002F OK\n\n    \u002F\u002F [...]\n    delete q;\n}\n",[928,1169,1170,1180,1189,1211,1215,1221,1226,1242,1246,1262,1277,1307,1313,1318,1323,1334,1343,1352,1373,1378,1384,1394],{"__ignoreMap":955},[959,1171,1172,1174,1176,1178],{"class":961,"line":962},[959,1173,966],{"class":965},[959,1175,970],{"class":969},[959,1177,974],{"class":973},[959,1179,977],{"class":969},[959,1181,1182,1184,1187],{"class":961,"line":980},[959,1183,996],{"class":995},[959,1185,1186],{"class":999}," Animal",[959,1188,1003],{"class":969},[959,1190,1191,1193,1196,1198,1201,1205,1208],{"class":961,"line":992},[959,1192,1009],{"class":995},[959,1194,1195],{"class":1012}," ~Animal",[959,1197,1016],{"class":969},[959,1199,1200],{"class":969}," =",[959,1202,1204],{"class":1203},"sbssI"," 0",[959,1206,1207],{"class":969},";",[959,1209,1210],{"class":1103}," \u002F\u002F 令 Animal 为抽象类\n",[959,1212,1213],{"class":961,"line":1006},[959,1214,1028],{"class":969},[959,1216,1217],{"class":961,"line":1025},[959,1218,1220],{"emptyLinePlaceholder":1219},true,"\n",[959,1222,1223],{"class":961,"line":1031},[959,1224,1225],{"class":1103},"\u002F\u002F 必须给出定义，原因见下\n",[959,1227,1228,1231,1234,1236,1238,1240],{"class":961,"line":1052},[959,1229,1230],{"class":999},"Animal",[959,1232,1233],{"class":969},"::~",[959,1235,1230],{"class":1012},[959,1237,1016],{"class":969},[959,1239,1019],{"class":969},[959,1241,1022],{"class":969},[959,1243,1244],{"class":961,"line":1065},[959,1245,1220],{"emptyLinePlaceholder":1219},[959,1247,1248,1250,1253,1255,1258,1260],{"class":961,"line":1086},[959,1249,996],{"class":995},[959,1251,1252],{"class":999}," Cat",[959,1254,1039],{"class":969},[959,1256,1257],{"class":995}," public",[959,1259,1186],{"class":999},[959,1261,1003],{"class":969},[959,1263,1264,1267,1270,1272,1275],{"class":961,"line":1107},[959,1265,1266],{"class":995},"    void",[959,1268,1269],{"class":1012}," meow",[959,1271,1016],{"class":969},[959,1273,1274],{"class":995}," const",[959,1276,1003],{"class":969},[959,1278,1279,1282,1284,1286,1288,1291,1294,1297,1299,1301,1303,1305],{"class":961,"line":1155},[959,1280,1281],{"class":999},"        std",[959,1283,1113],{"class":969},[959,1285,1116],{"class":1042},[959,1287,1119],{"class":969},[959,1289,1290],{"class":969}," \"",[959,1292,1293],{"class":973},"meow~",[959,1295,1296],{"class":969},"\"",[959,1298,1141],{"class":969},[959,1300,1144],{"class":999},[959,1302,1113],{"class":969},[959,1304,1149],{"class":1042},[959,1306,1152],{"class":969},[959,1308,1310],{"class":961,"line":1309},12,[959,1311,1312],{"class":969},"    }\n",[959,1314,1316],{"class":961,"line":1315},13,[959,1317,1028],{"class":969},[959,1319,1321],{"class":961,"line":1320},14,[959,1322,1220],{"emptyLinePlaceholder":1219},[959,1324,1326,1328,1330,1332],{"class":961,"line":1325},15,[959,1327,1055],{"class":995},[959,1329,1058],{"class":1012},[959,1331,1016],{"class":969},[959,1333,1003],{"class":969},[959,1335,1337,1340],{"class":961,"line":1336},16,[959,1338,1339],{"class":1103},"    \u002F\u002F Animal a;",[959,1341,1342],{"class":1103},"                \u002F\u002F 编译错误\n",[959,1344,1346,1349],{"class":961,"line":1345},17,[959,1347,1348],{"class":1103},"    \u002F\u002F Animal* p{new Animal{}};",[959,1350,1351],{"class":1103}," \u002F\u002F 编译错误\n",[959,1353,1355,1358,1360,1363,1365,1367,1370],{"class":961,"line":1354},18,[959,1356,1357],{"class":1068},"    Animal",[959,1359,1072],{"class":969},[959,1361,1362],{"class":1068}," q",[959,1364,1078],{"class":969},[959,1366,1252],{"class":1042},[959,1368,1369],{"class":969},"{}};",[959,1371,1372],{"class":1103},"       \u002F\u002F OK\n",[959,1374,1376],{"class":961,"line":1375},19,[959,1377,1220],{"emptyLinePlaceholder":1219},[959,1379,1381],{"class":961,"line":1380},20,[959,1382,1383],{"class":1103},"    \u002F\u002F [...]\n",[959,1385,1387,1390,1392],{"class":961,"line":1386},21,[959,1388,1389],{"class":969},"    delete",[959,1391,1362],{"class":1068},[959,1393,1152],{"class":969},[959,1395,1397],{"class":961,"line":1396},22,[959,1398,1158],{"class":969},[918,1400,1401,1402,1406,1407,1410,1411,1414,1415,1420,1421,1423,1424,1426],{},"但请务必注意，在上面的代码中，我们",[1403,1404,1405],"strong",{},"必须定义"," ",[928,1408,1409],{},"Animal::~Animal","。因为在释放 ",[928,1412,1413],{},"Cat"," 类型对象时，程序",[1416,1417,1419],"a",{"href":1418},"\u002Fch07\u002Finheritance\u002Fmisc#%E5%86%8D%E8%B0%88%E9%A2%84%E7%BD%AE%E5%87%BD%E6%95%B0","会去调用","基类 ",[928,1422,1230],{}," 的析构函数；若只声明却不定义 ",[928,1425,1409],{}," 会得到链接错误。",[943,1428,1429],{"id":1429},"资源安全性",[918,1431,1432],{},"考虑以下代码：",[950,1434,1436],{"className":952,"code":1435,"language":954,"meta":955,"style":955},"#include \u003Ciostream>\nstruct Base { };\nstruct Derived : Base {\nprivate:\n    char* p;\n\npublic:\n    Derived(unsigned size) {\n        p = new char[size];\n        std::cout \u003C\u003C \"ctor called\" \u003C\u003C std::endl;\n    }\n    ~Derived() {\n        delete[] p;\n        std::cout \u003C\u003C \"dtor called\" \u003C\u003C std::endl;\n    }\n};\n\nint main() {\n    Base* b{nullptr};\n    b = new Derived(16);\n    \u002F\u002F [...]\n    delete b;\n}\n",[928,1437,1438,1448,1458,1471,1479,1490,1494,1501,1520,1543,1570,1574,1583,1592,1619,1623,1627,1631,1641,1653,1672,1676,1684],{"__ignoreMap":955},[959,1439,1440,1442,1444,1446],{"class":961,"line":962},[959,1441,966],{"class":965},[959,1443,970],{"class":969},[959,1445,974],{"class":973},[959,1447,977],{"class":969},[959,1449,1450,1452,1454,1456],{"class":961,"line":980},[959,1451,996],{"class":995},[959,1453,1000],{"class":999},[959,1455,1019],{"class":969},[959,1457,1049],{"class":969},[959,1459,1460,1462,1464,1466,1468],{"class":961,"line":992},[959,1461,996],{"class":995},[959,1463,1036],{"class":999},[959,1465,1039],{"class":969},[959,1467,1043],{"class":1042},[959,1469,1470],{"class":969},"{\n",[959,1472,1473,1476],{"class":961,"line":1006},[959,1474,1475],{"class":995},"private",[959,1477,1478],{"class":969},":\n",[959,1480,1481,1484,1486,1488],{"class":961,"line":1025},[959,1482,1483],{"class":995},"    char",[959,1485,1072],{"class":969},[959,1487,1075],{"class":1042},[959,1489,1152],{"class":969},[959,1491,1492],{"class":961,"line":1031},[959,1493,1220],{"emptyLinePlaceholder":1219},[959,1495,1496,1499],{"class":961,"line":1052},[959,1497,1498],{"class":995},"public",[959,1500,1478],{"class":969},[959,1502,1503,1506,1509,1512,1516,1518],{"class":961,"line":1065},[959,1504,1505],{"class":1012},"    Derived",[959,1507,1508],{"class":969},"(",[959,1510,1511],{"class":995},"unsigned",[959,1513,1515],{"class":1514},"sHdIc"," size",[959,1517,1127],{"class":969},[959,1519,1003],{"class":969},[959,1521,1522,1525,1528,1531,1534,1537,1540],{"class":961,"line":1086},[959,1523,1524],{"class":1042},"        p ",[959,1526,1527],{"class":969},"=",[959,1529,1530],{"class":969}," new",[959,1532,1533],{"class":995}," char",[959,1535,1536],{"class":969},"[",[959,1538,1539],{"class":1042},"size",[959,1541,1542],{"class":969},"];\n",[959,1544,1545,1547,1549,1551,1553,1555,1558,1560,1562,1564,1566,1568],{"class":961,"line":1107},[959,1546,1281],{"class":999},[959,1548,1113],{"class":969},[959,1550,1116],{"class":1042},[959,1552,1119],{"class":969},[959,1554,1290],{"class":969},[959,1556,1557],{"class":973},"ctor called",[959,1559,1296],{"class":969},[959,1561,1141],{"class":969},[959,1563,1144],{"class":999},[959,1565,1113],{"class":969},[959,1567,1149],{"class":1042},[959,1569,1152],{"class":969},[959,1571,1572],{"class":961,"line":1155},[959,1573,1312],{"class":969},[959,1575,1576,1579,1581],{"class":961,"line":1309},[959,1577,1578],{"class":1012},"    ~Derived",[959,1580,1016],{"class":969},[959,1582,1003],{"class":969},[959,1584,1585,1588,1590],{"class":961,"line":1315},[959,1586,1587],{"class":969},"        delete[]",[959,1589,1075],{"class":1042},[959,1591,1152],{"class":969},[959,1593,1594,1596,1598,1600,1602,1604,1607,1609,1611,1613,1615,1617],{"class":961,"line":1320},[959,1595,1281],{"class":999},[959,1597,1113],{"class":969},[959,1599,1116],{"class":1042},[959,1601,1119],{"class":969},[959,1603,1290],{"class":969},[959,1605,1606],{"class":973},"dtor called",[959,1608,1296],{"class":969},[959,1610,1141],{"class":969},[959,1612,1144],{"class":999},[959,1614,1113],{"class":969},[959,1616,1149],{"class":1042},[959,1618,1152],{"class":969},[959,1620,1621],{"class":961,"line":1325},[959,1622,1312],{"class":969},[959,1624,1625],{"class":961,"line":1336},[959,1626,1028],{"class":969},[959,1628,1629],{"class":961,"line":1345},[959,1630,1220],{"emptyLinePlaceholder":1219},[959,1632,1633,1635,1637,1639],{"class":961,"line":1354},[959,1634,1055],{"class":995},[959,1636,1058],{"class":1012},[959,1638,1016],{"class":969},[959,1640,1003],{"class":969},[959,1642,1643,1645,1647,1650],{"class":961,"line":1375},[959,1644,1069],{"class":1068},[959,1646,1072],{"class":969},[959,1648,1649],{"class":1068}," b",[959,1651,1652],{"class":969},"{nullptr};\n",[959,1654,1655,1658,1660,1662,1664,1666,1669],{"class":961,"line":1380},[959,1656,1657],{"class":1068},"    b ",[959,1659,1527],{"class":969},[959,1661,1530],{"class":969},[959,1663,1036],{"class":1012},[959,1665,1508],{"class":969},[959,1667,1668],{"class":1203},"16",[959,1670,1671],{"class":969},");\n",[959,1673,1674],{"class":961,"line":1386},[959,1675,1383],{"class":1103},[959,1677,1678,1680,1682],{"class":961,"line":1396},[959,1679,1389],{"class":969},[959,1681,1649],{"class":1068},[959,1683,1152],{"class":969},[959,1685,1687],{"class":961,"line":1686},23,[959,1688,1158],{"class":969},[918,1690,1691,1692,1694,1695,1698,1699,1701,1702,1705,1706,1708,1709,1711,1712,1714,1715,1717],{},"这段代码中，",[928,1693,1092],{}," 继承了 ",[928,1696,1697],{},"Base","，并拥有一个指针 ",[928,1700,918],{}," 可以指向一片 ",[928,1703,1704],{},"new"," 出来的内存。",[928,1707,918],{}," 所指向的内存会在 ",[928,1710,1092],{}," 构造时申请得到，在 ",[928,1713,1092],{}," 析构时释放。然后，main 函数中用多态的风格使用了 ",[928,1716,1092],{},"。一切看上去都很不错，但这段程序只会输出：",[1719,1720,1721],"io-block",{},[918,1722,1557],{},[918,1724,1725,1726,1729],{},"也就是说，",[928,1727,1728],{},"~Derived"," 的析构函数根本没被执行。这是为什么呢？",[918,1731,1732,1733,1736,1737,1740,1741,1743,1744,1747,1748,1751,1752,1754,1755,1758,1759,1762,1763,1766,1767,1769,1770,1773],{},"问题的根源在 ",[928,1734,1735],{},"delete b"," 这个表达式的执行上。执行 ",[928,1738,1739],{},"delete"," 会调用操作数所指向对象的析构函数，即 ",[928,1742,1735],{}," 在释放其内存前掉用 ",[928,1745,1746],{},"b->~Base()","。这里调用 ",[928,1749,1750],{},"~Base"," 而非 ",[928,1753,1728],{}," 的原因正是 ",[928,1756,1757],{},"b"," 是 ",[928,1760,1761],{},"Base*"," 类型而非 ",[928,1764,1765],{},"Derived*"," 类型的。因此，整个析构过程中，",[928,1768,1728],{}," 根本无法得到调用。造成的后果就是 ",[928,1771,1772],{},"Derived::p"," 所指向的内存没被释放，一个内存泄漏出现了。",[918,1775,1776],{},"这很不好。那有什么解决办法呢？注意到这里的情形和之前引入虚函数的例子很像——期望调用派生类函数的场景却调用了基类的函数。所以方法就是：将析构函数设置为虚函数。",[950,1778,1780],{"className":952,"code":1779,"language":954,"meta":955,"style":955},"#include \u003Ciostream>\nstruct Base {\n    \u002F\u002F 写空函数体也行，和 =default 效果一样\n    virtual ~Base() = default;\n};\nstruct Derived : Base {\nprivate:\n    char* p;\n\npublic:\n    Derived(unsigned size) {\n        p = new char[size];\n        std::cout \u003C\u003C \"ctor called\" \u003C\u003C std::endl;\n    }\n    ~Derived() {\n        delete[] p;\n        std::cout \u003C\u003C \"dtor called\" \u003C\u003C std::endl;\n    }\n};\n\nint main() {\n    Base* b{nullptr};\n    b = new Derived(16);\n    \u002F\u002F [...]\n    delete b;\n}\n",[928,1781,1782,1792,1800,1805,1820,1824,1836,1842,1852,1856,1862,1876,1892,1918,1922,1930,1938,1964,1968,1972,1976,1986,1996,2012,2017,2026],{"__ignoreMap":955},[959,1783,1784,1786,1788,1790],{"class":961,"line":962},[959,1785,966],{"class":965},[959,1787,970],{"class":969},[959,1789,974],{"class":973},[959,1791,977],{"class":969},[959,1793,1794,1796,1798],{"class":961,"line":980},[959,1795,996],{"class":995},[959,1797,1000],{"class":999},[959,1799,1003],{"class":969},[959,1801,1802],{"class":961,"line":992},[959,1803,1804],{"class":1103},"    \u002F\u002F 写空函数体也行，和 =default 效果一样\n",[959,1806,1807,1809,1811,1813,1815,1818],{"class":961,"line":1006},[959,1808,1009],{"class":995},[959,1810,1013],{"class":1012},[959,1812,1016],{"class":969},[959,1814,1200],{"class":969},[959,1816,1817],{"class":1203}," default",[959,1819,1152],{"class":969},[959,1821,1822],{"class":961,"line":1025},[959,1823,1028],{"class":969},[959,1825,1826,1828,1830,1832,1834],{"class":961,"line":1031},[959,1827,996],{"class":995},[959,1829,1036],{"class":999},[959,1831,1039],{"class":969},[959,1833,1043],{"class":1042},[959,1835,1470],{"class":969},[959,1837,1838,1840],{"class":961,"line":1052},[959,1839,1475],{"class":995},[959,1841,1478],{"class":969},[959,1843,1844,1846,1848,1850],{"class":961,"line":1065},[959,1845,1483],{"class":995},[959,1847,1072],{"class":969},[959,1849,1075],{"class":1042},[959,1851,1152],{"class":969},[959,1853,1854],{"class":961,"line":1086},[959,1855,1220],{"emptyLinePlaceholder":1219},[959,1857,1858,1860],{"class":961,"line":1107},[959,1859,1498],{"class":995},[959,1861,1478],{"class":969},[959,1863,1864,1866,1868,1870,1872,1874],{"class":961,"line":1155},[959,1865,1505],{"class":1012},[959,1867,1508],{"class":969},[959,1869,1511],{"class":995},[959,1871,1515],{"class":1514},[959,1873,1127],{"class":969},[959,1875,1003],{"class":969},[959,1877,1878,1880,1882,1884,1886,1888,1890],{"class":961,"line":1309},[959,1879,1524],{"class":1042},[959,1881,1527],{"class":969},[959,1883,1530],{"class":969},[959,1885,1533],{"class":995},[959,1887,1536],{"class":969},[959,1889,1539],{"class":1042},[959,1891,1542],{"class":969},[959,1893,1894,1896,1898,1900,1902,1904,1906,1908,1910,1912,1914,1916],{"class":961,"line":1315},[959,1895,1281],{"class":999},[959,1897,1113],{"class":969},[959,1899,1116],{"class":1042},[959,1901,1119],{"class":969},[959,1903,1290],{"class":969},[959,1905,1557],{"class":973},[959,1907,1296],{"class":969},[959,1909,1141],{"class":969},[959,1911,1144],{"class":999},[959,1913,1113],{"class":969},[959,1915,1149],{"class":1042},[959,1917,1152],{"class":969},[959,1919,1920],{"class":961,"line":1320},[959,1921,1312],{"class":969},[959,1923,1924,1926,1928],{"class":961,"line":1325},[959,1925,1578],{"class":1012},[959,1927,1016],{"class":969},[959,1929,1003],{"class":969},[959,1931,1932,1934,1936],{"class":961,"line":1336},[959,1933,1587],{"class":969},[959,1935,1075],{"class":1042},[959,1937,1152],{"class":969},[959,1939,1940,1942,1944,1946,1948,1950,1952,1954,1956,1958,1960,1962],{"class":961,"line":1345},[959,1941,1281],{"class":999},[959,1943,1113],{"class":969},[959,1945,1116],{"class":1042},[959,1947,1119],{"class":969},[959,1949,1290],{"class":969},[959,1951,1606],{"class":973},[959,1953,1296],{"class":969},[959,1955,1141],{"class":969},[959,1957,1144],{"class":999},[959,1959,1113],{"class":969},[959,1961,1149],{"class":1042},[959,1963,1152],{"class":969},[959,1965,1966],{"class":961,"line":1354},[959,1967,1312],{"class":969},[959,1969,1970],{"class":961,"line":1375},[959,1971,1028],{"class":969},[959,1973,1974],{"class":961,"line":1380},[959,1975,1220],{"emptyLinePlaceholder":1219},[959,1977,1978,1980,1982,1984],{"class":961,"line":1386},[959,1979,1055],{"class":995},[959,1981,1058],{"class":1012},[959,1983,1016],{"class":969},[959,1985,1003],{"class":969},[959,1987,1988,1990,1992,1994],{"class":961,"line":1396},[959,1989,1069],{"class":1068},[959,1991,1072],{"class":969},[959,1993,1649],{"class":1068},[959,1995,1652],{"class":969},[959,1997,1998,2000,2002,2004,2006,2008,2010],{"class":961,"line":1686},[959,1999,1657],{"class":1068},[959,2001,1527],{"class":969},[959,2003,1530],{"class":969},[959,2005,1036],{"class":1012},[959,2007,1508],{"class":969},[959,2009,1668],{"class":1203},[959,2011,1671],{"class":969},[959,2013,2015],{"class":961,"line":2014},24,[959,2016,1383],{"class":1103},[959,2018,2020,2022,2024],{"class":961,"line":2019},25,[959,2021,1389],{"class":969},[959,2023,1649],{"class":1068},[959,2025,1152],{"class":969},[959,2027,2029],{"class":961,"line":2028},26,[959,2030,1158],{"class":969},[918,2032,2033,2034,2036,2037,2039,2040,2042,2043,2046],{},"这段代码就能正确输出 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