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}\n",[922,1156,1157,1165,1171,1179,1189,1194,1237,1241,1247,1252,1257,1263],{"__ignoreMap":939},[943,1158,1159,1161,1163],{"class":945,"line":946},[943,1160,950],{"class":949},[943,1162,954],{"class":953},[943,1164,958],{"class":957},[943,1166,1167,1169],{"class":945,"line":961},[943,1168,964],{"class":949},[943,1170,967],{"class":957},[943,1172,1173,1175,1177],{"class":945,"line":970},[943,1174,973],{"class":949},[943,1176,977],{"class":976},[943,1178,980],{"class":957},[943,1180,1181,1183,1185,1187],{"class":945,"line":983},[943,1182,986],{"class":949},[943,1184,989],{"class":957},[943,1186,992],{"class":976},[943,1188,980],{"class":957},[943,1190,1191],{"class":945,"line":997},[943,1192,1193],{"class":1015},"    \u002F\u002F 照抄下来的声明 + friend 关键字\n",[943,1195,1196,1199,1202,1204,1206,1208,1210,1212,1214,1216,1218,1220,1222,1224,1226,1228,1230,1232,1234],{"class":945,"line":1004},[943,1197,1198],{"class":949},"    friend",[943,1200,1201],{"class":953}," std",[943,1203,1031],{"class":957},[943,1205,1034],{"class":953},[943,1207,1037],{"class":949},[943,1209,1041],{"class":1040},[943,1211,1044],{"class":953},[943,1213,1047],{"class":957},[943,1215,1028],{"class":953},[943,1217,1031],{"class":957},[943,1219,1034],{"class":953},[943,1221,1037],{"class":949},[943,1223,1059],{"class":1058},[943,1225,1062],{"class":957},[943,1227,1065],{"class":949},[943,1229,954],{"class":953},[943,1231,1037],{"class":949},[943,1233,1072],{"class":1058},[943,1235,1236],{"class":957},");\n",[943,1238,1239],{"class":945,"line":1012},[943,1240,1001],{"emptyLinePlaceholder":1000},[943,1242,1243,1245],{"class":945,"line":1019},[943,1244,1007],{"class":949},[943,1246,967],{"class":957},[943,1248,1249],{"class":945,"line":1025},[943,1250,1251],{"class":1015},"    \u002F\u002F [...]\n",[943,1253,1255],{"class":945,"line":1254},10,[943,1256,1022],{"class":957},[943,1258,1260],{"class":945,"line":1259},11,[943,1261,1262],{"class":1015},"\u002F\u002F 函数定义保持不动\n",[943,1264,1266,1268,1270,1272,1274,1276,1278,1280,1282,1284,1286,1288,1290,1292,1294,1296,1298,1300,1302,1304,1306],{"class":945,"line":1265},12,[943,1267,1028],{"class":953},[943,1269,1031],{"class":957},[943,1271,1034],{"class":953},[943,1273,1037],{"class":949},[943,1275,1041],{"class":1040},[943,1277,1044],{"class":953},[943,1279,1047],{"class":957},[943,1281,1028],{"class":953},[943,1283,1031],{"class":957},[943,1285,1034],{"class":953},[943,1287,1037],{"class":949},[943,1289,1059],{"class":1058},[943,1291,1062],{"class":957},[943,1293,1065],{"class":949},[943,1295,954],{"class":953},[943,1297,1037],{"class":949},[943,1299,1072],{"class":1058},[943,1301,1075],{"class":957},[943,1303,1078],{"class":957},[943,1305,1081],{"class":1015},[943,1307,1084],{"class":957},[918,1309,1310,1311,1313,1314,1317,1318,1321,1322,1325],{},"现在就没有编译错误了。需要注意的是，成员列表里 ",[922,1312,1141],{}," 开头的声明（称为友元声明）",[1093,1315,1316],{},"不是","这个类的成员，所以访问说明符 ",[922,1319,1320],{},"public:"," 还是 ",[922,1323,1324],{},"private:"," 对其没有影响。",[918,1327,1328],{},"可以声明另一个类为友元：",[934,1330,1332],{"className":936,"code":1331,"language":938,"meta":939,"style":939},"class A {\nprivate:\n    int privateMem;\n    friend class B; \u002F\u002F 友元声明\n};\nclass B {\n    void f() {\n        A a;\n        a.privateMem = 0; \u002F\u002F 可以访问私有成员\n    }\n};\nint main() { }\n",[922,1333,1334,1343,1349,1359,1375,1379,1387,1401,1408,1431,1436,1440],{"__ignoreMap":939},[943,1335,1336,1338,1341],{"class":945,"line":946},[943,1337,950],{"class":949},[943,1339,1340],{"class":953}," A",[943,1342,958],{"class":957},[943,1344,1345,1347],{"class":945,"line":961},[943,1346,964],{"class":949},[943,1348,967],{"class":957},[943,1350,1351,1354,1357],{"class":945,"line":970},[943,1352,1353],{"class":949},"    int",[943,1355,1356],{"class":976}," privateMem",[943,1358,980],{"class":957},[943,1360,1361,1363,1366,1369,1372],{"class":945,"line":983},[943,1362,1198],{"class":949},[943,1364,1365],{"class":949}," class",[943,1367,1368],{"class":953}," B",[943,1370,1371],{"class":957},";",[943,1373,1374],{"class":1015}," \u002F\u002F 友元声明\n",[943,1376,1377],{"class":945,"line":997},[943,1378,1022],{"class":957},[943,1380,1381,1383,1385],{"class":945,"line":1004},[943,1382,950],{"class":949},[943,1384,1368],{"class":953},[943,1386,958],{"class":957},[943,1388,1389,1392,1396,1399],{"class":945,"line":1012},[943,1390,1391],{"class":949},"    void",[943,1393,1395],{"class":1394},"s2Zo4"," f",[943,1397,1398],{"class":957},"()",[943,1400,958],{"class":957},[943,1402,1403,1406],{"class":945,"line":1019},[943,1404,1405],{"class":976},"        A a",[943,1407,980],{"class":957},[943,1409,1410,1414,1417,1420,1423,1426,1428],{"class":945,"line":1025},[943,1411,1413],{"class":1412},"sTEyZ","        a",[943,1415,1416],{"class":957},".",[943,1418,1419],{"class":1412},"privateMem",[943,1421,1422],{"class":957}," =",[943,1424,1425],{"class":1040}," 0",[943,1427,1371],{"class":957},[943,1429,1430],{"class":1015}," \u002F\u002F 可以访问私有成员\n",[943,1432,1433],{"class":945,"line":1254},[943,1434,1435],{"class":957},"    }\n",[943,1437,1438],{"class":945,"line":1259},[943,1439,1022],{"class":957},[943,1441,1442,1445,1448,1450,1452],{"class":945,"line":1265},[943,1443,1444],{"class":949},"int",[943,1446,1447],{"class":1394}," main",[943,1449,1398],{"class":957},[943,1451,1078],{"class":957},[943,1453,1084],{"class":957},[918,1455,1456,1457,1460,1461,1463,1464,1467,1468,1115],{},"在这个例子中，类 ",[922,1458,1459],{},"B"," 被声明为类 ",[922,1462,1125],{}," 的友元：方法很简单，把声明 ",[922,1465,1466],{},"class B"," 抄下然后加上 ",[922,1469,1141],{},[918,1471,1472],{},"也可以声明另一个类的某个成员函数为友元：",[934,1474,1476],{"className":936,"code":1475,"language":938,"meta":939,"style":939},"struct B {\n    void f(); \u002F\u002F 定义见下\n};\n\nclass A {     \u002F\u002F 这里需要 B 的定义，所以要放在 B 下面\nprivate:\n    int privateMem;\n    friend void B::f(); \u002F\u002F 友元声明\n};\n\nvoid B::f() { \u002F\u002F 这里需要 A 的定义，所以要放在 A 下面\n    A a;\n    a.privateMem = 0;   \u002F\u002F 可以访问私有成员\n}\n\nint main() { }\n",[922,1477,1478,1487,1499,1503,1507,1518,1524,1532,1549,1553,1557,1575,1582,1603,1609,1614],{"__ignoreMap":939},[943,1479,1480,1483,1485],{"class":945,"line":946},[943,1481,1482],{"class":949},"struct",[943,1484,1368],{"class":953},[943,1486,958],{"class":957},[943,1488,1489,1491,1493,1496],{"class":945,"line":961},[943,1490,1391],{"class":949},[943,1492,1395],{"class":1394},[943,1494,1495],{"class":957},"();",[943,1497,1498],{"class":1015}," \u002F\u002F 定义见下\n",[943,1500,1501],{"class":945,"line":970},[943,1502,1022],{"class":957},[943,1504,1505],{"class":945,"line":983},[943,1506,1001],{"emptyLinePlaceholder":1000},[943,1508,1509,1511,1513,1515],{"class":945,"line":997},[943,1510,950],{"class":949},[943,1512,1340],{"class":953},[943,1514,1078],{"class":957},[943,1516,1517],{"class":1015},"     \u002F\u002F 这里需要 B 的定义，所以要放在 B 下面\n",[943,1519,1520,1522],{"class":945,"line":1004},[943,1521,964],{"class":949},[943,1523,967],{"class":957},[943,1525,1526,1528,1530],{"class":945,"line":1012},[943,1527,1353],{"class":949},[943,1529,1356],{"class":976},[943,1531,980],{"class":957},[943,1533,1534,1536,1539,1541,1543,1545,1547],{"class":945,"line":1019},[943,1535,1198],{"class":949},[943,1537,1538],{"class":949}," void",[943,1540,1368],{"class":953},[943,1542,1031],{"class":957},[943,1544,1121],{"class":1394},[943,1546,1495],{"class":957},[943,1548,1374],{"class":1015},[943,1550,1551],{"class":945,"line":1025},[943,1552,1022],{"class":957},[943,1554,1555],{"class":945,"line":1254},[943,1556,1001],{"emptyLinePlaceholder":1000},[943,1558,1559,1562,1564,1566,1568,1570,1572],{"class":945,"line":1259},[943,1560,1561],{"class":949},"void",[943,1563,1368],{"class":953},[943,1565,1031],{"class":957},[943,1567,1121],{"class":1394},[943,1569,1398],{"class":957},[943,1571,1078],{"class":957},[943,1573,1574],{"class":1015}," \u002F\u002F 这里需要 A 的定义，所以要放在 A 下面\n",[943,1576,1577,1580],{"class":945,"line":1265},[943,1578,1579],{"class":1412},"    A a",[943,1581,980],{"class":957},[943,1583,1585,1588,1590,1593,1596,1598,1600],{"class":945,"line":1584},13,[943,1586,1587],{"class":1412},"    a",[943,1589,1416],{"class":957},[943,1591,1592],{"class":1412},"privateMem ",[943,1594,1595],{"class":957},"=",[943,1597,1425],{"class":1040},[943,1599,1371],{"class":957},[943,1601,1602],{"class":1015},"   \u002F\u002F 可以访问私有成员\n",[943,1604,1606],{"class":945,"line":1605},14,[943,1607,1608],{"class":957},"}\n",[943,1610,1612],{"class":945,"line":1611},15,[943,1613,1001],{"emptyLinePlaceholder":1000},[943,1615,1617,1619,1621,1623,1625],{"class":945,"line":1616},16,[943,1618,1444],{"class":949},[943,1620,1447],{"class":1394},[943,1622,1398],{"class":957},[943,1624,1078],{"class":957},[943,1626,1084],{"class":957},[918,1628,1629,1630,1632,1633,1129,1635,1637,1638,1641,1642,1644,1645,1648,1649,1651,1652,1654,1655,1657,1658,1660,1661,1663,1664,1667,1668,1670,1671,1115],{},"如果想要让 ",[922,1631,1459],{}," 的成员函数 ",[922,1634,1121],{},[922,1636,1125],{}," 的友元，则需要写 ",[922,1639,1640],{},"friend void B::f();","：除了前面加上 ",[922,1643,1141],{}," 以外，需要类似类外定义函数一样加上 ",[922,1646,1647],{},"B::"," 这个东西。然而为了让编译器知道 ",[922,1650,1459],{}," 是个什么，你必须要把 ",[922,1653,1459],{}," 的定义放在友元声明前面；另一方面为了让 ",[922,1656,1459],{}," 中的 ",[922,1659,1121],{}," 函数能用 ",[922,1662,1125],{}," 的成员，你还要把 ",[922,1665,1666],{},"B::f"," 的定义放在 ",[922,1669,1125],{}," 的定义后面。所以这种情形你恐怕必须要类外定义 ",[922,1672,1121],{},[918,1674,1675],{},"最后，介绍一种写法：你可以把友元函数的定义也放在类里面。",[934,1677,1679],{"className":936,"code":1678,"language":938,"meta":939,"style":939},"class String {\nprivate:\n    unsigned len;\n    char* str;\n    \u002F\u002F friend 关键字 + 函数定义\n    friend std::ostream& operator\u003C\u003C(std::ostream& os, const String& b) {\n        os \u003C\u003C b.str;\n        return os;\n    }\n\npublic:\n    \u002F\u002F [...]\n};\n\u002F\u002F 就不需要在全局定义 operator\u003C\u003C 了\n",[922,1680,1681,1689,1695,1703,1713,1718,1760,1775,1785,1789,1793,1799,1803,1807],{"__ignoreMap":939},[943,1682,1683,1685,1687],{"class":945,"line":946},[943,1684,950],{"class":949},[943,1686,954],{"class":953},[943,1688,958],{"class":957},[943,1690,1691,1693],{"class":945,"line":961},[943,1692,964],{"class":949},[943,1694,967],{"class":957},[943,1696,1697,1699,1701],{"class":945,"line":970},[943,1698,973],{"class":949},[943,1700,977],{"class":976},[943,1702,980],{"class":957},[943,1704,1705,1707,1709,1711],{"class":945,"line":983},[943,1706,986],{"class":949},[943,1708,989],{"class":957},[943,1710,992],{"class":976},[943,1712,980],{"class":957},[943,1714,1715],{"class":945,"line":997},[943,1716,1717],{"class":1015},"    \u002F\u002F friend 关键字 + 函数定义\n",[943,1719,1720,1722,1724,1726,1728,1730,1732,1734,1736,1738,1740,1742,1744,1746,1748,1750,1752,1754,1756,1758],{"class":945,"line":1004},[943,1721,1198],{"class":949},[943,1723,1201],{"class":953},[943,1725,1031],{"class":957},[943,1727,1034],{"class":953},[943,1729,1037],{"class":949},[943,1731,1041],{"class":1040},[943,1733,1044],{"class":953},[943,1735,1047],{"class":957},[943,1737,1028],{"class":953},[943,1739,1031],{"class":957},[943,1741,1034],{"class":953},[943,1743,1037],{"class":949},[943,1745,1059],{"class":1058},[943,1747,1062],{"class":957},[943,1749,1065],{"class":949},[943,1751,954],{"class":953},[943,1753,1037],{"class":949},[943,1755,1072],{"class":1058},[943,1757,1075],{"class":957},[943,1759,958],{"class":957},[943,1761,1762,1765,1767,1769,1771,1773],{"class":945,"line":1012},[943,1763,1764],{"class":976},"        os ",[943,1766,1044],{"class":957},[943,1768,1072],{"class":1412},[943,1770,1416],{"class":957},[943,1772,928],{"class":1412},[943,1774,980],{"class":957},[943,1776,1777,1781,1783],{"class":945,"line":1019},[943,1778,1780],{"class":1779},"s7zQu","        return",[943,1782,1059],{"class":976},[943,1784,980],{"class":957},[943,1786,1787],{"class":945,"line":1025},[943,1788,1435],{"class":957},[943,1790,1791],{"class":945,"line":1254},[943,1792,1001],{"emptyLinePlaceholder":1000},[943,1794,1795,1797],{"class":945,"line":1259},[943,1796,1007],{"class":949},[943,1798,967],{"class":957},[943,1800,1801],{"class":945,"line":1265},[943,1802,1251],{"class":1015},[943,1804,1805],{"class":945,"line":1584},[943,1806,1022],{"class":957},[943,1808,1809],{"class":945,"line":1605},[943,1810,1811],{"class":1015},"\u002F\u002F 就不需要在全局定义 operator\u003C\u003C 了\n",[918,1813,1814,1815,1817,1818,1821],{},"这样做可以节省一些代码量，但这样很容易让人误以为 ",[922,1816,1090],{}," 是一个成员函数。然而事实并不是这样的，我们只是把它本来在全局的函数定义放到类里面去了而已：它没有 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