{"id":383,"date":"2017-11-04T13:43:30","date_gmt":"2017-11-04T05:43:30","guid":{"rendered":"https:\/\/colliot.me\/?p=383"},"modified":"2017-11-23T23:45:51","modified_gmt":"2017-11-23T15:45:51","slug":"%e4%be%8b%e8%af%b4-c-%e8%af%ad%e8%a8%80%e7%b1%bb%e5%9e%8b%e5%a3%b0%e6%98%8e","status":"publish","type":"post","link":"https:\/\/colliot.org\/en\/2017\/11\/%e4%be%8b%e8%af%b4-c-%e8%af%ad%e8%a8%80%e7%b1%bb%e5%9e%8b%e5%a3%b0%e6%98%8e\/","title":{"rendered":"Demystifying the Type Declarations in C"},"content":{"rendered":"

<\/p>\n

The type declarations in C, restricted by C’s long history, appears rather complicated in many situations. Let’s give it a thorough analysis today.<\/div>\n
\n

Pointers and Arrays<\/h1>\n

Nested Once<\/h2>\n

Even the very beginners wouldn’t find the following problems hard:<\/p>\n

Are you able to declare an array?<\/p>\n

int a[5]; \/\/ With 5 elements.<\/pre>\n
Are you able to declare a pointer?<\/p>\n
int *a;<\/pre>\n
Nested Twice<\/h2>\n
Are you able to declare a nested pointer?<\/p>\n
<\/p>\n
int **a;<\/pre>\n
\u4f60\u4f1a\u58f0\u660e\u4e8c\u7ef4\u6570\u7ec4\u5417\uff1f<\/p>\n
\/\/ \u7b2c\u4e00\u7ef4\u957f 5\uff0c\u7b2c\u4e8c\u7ef4\u957f 7\r\nint a[5][7];<\/pre>\n
\u90a3\u4f60\u4f1a\u58f0\u660e\u6307\u9488\u7684\u6570\u7ec4\u5417\uff1f<\/p>\n
\/\/ \u6570\u7ec4\u7684\u957f\u5ea6\u4e3a 7\r\nint *a[7];<\/pre>\n
\u4f60\u4f1a\u58f0\u660e\uff08\u6307\u5411\uff09\u6570\u7ec4\u7684\u6307\u9488\u5417\uff1f<\/p>\n
int (*a)[5];<\/pre>\n
\u601d\u8003\u9898 1<\/b>\uff1a\u4e8c\u7ef4\u6570\u7ec4\u3001\u6570\u7ec4\u7684\u6307\u9488\u3001\u6307\u9488\u7684\u6570\u7ec4\uff0c\u8fd9\u4e9b\u4e1c\u897f\u662f\u4e00\u6837\u7684\u5417\uff1f\u6709\u76f8\u540c\u7684\u5417\uff1f\u8fd8\u662f\u5404\u4e0d\u76f8\u540c\uff1f<\/p>\n
\u7b54\u6848\uff1a\u53ef\u53c2\u8003\u300a\u8bf4\u51fa\u6765\u4f60\u4eec\u53ef\u80fd\u4e0d\u4fe1\uff0c\u4f46\u662f\u6570\u7ec4\u540d\u786e\u5b9e\u4e0d\u662f\u6307\u9488\u5e38\u91cf\u300b<\/a>\u3002\u4ee5\u540e\u6211\u4e5f\u53ef\u80fd\u4f1a\u5199\u3002<\/p>\n
\u4e00\u5b9a\u8981\u6ce8\u610f\uff0c\u7528\u6307\u9488\u7c7b\u578b\u4ee3\u66ff\u6570\u7ec4\u662f\u9519\u8bef\u7684\u505a\u6cd5\u2014\u2014\u5bf9\u4e8e\u591a\u91cd\u6570\u7ec4\u548c\u591a\u91cd\u6307\u9488\uff0c\u5b83\u4eec\u4e0b\u6807\u7684\u8bed\u4e49\u662f\u4e0d\u4e00\u6837\u7684\u3002\u65e0\u8bba\u51e0\u7ef4\u6570\u7ec4\uff0c\u5b83\u4eec\u7684\u5185\u5b58\u5e03\u5c40\u603b\u662f\u7ebf\u6027\u7684\uff0c\u6307\u9488\u5374\u4e0d\u7136\uff0c\u6709\u591a\u5c11\u91cd\u5c31\u4f1a\u771f\u7684\u505a\u591a\u5c11\u6b21\u8df3\u8f6c\u3002<\/p>\n
\u4e09\u91cd\u58f0\u660e<\/h2>\n
\u4f60\u4f1a\u58f0\u660e\u3010\u6570\u7ec4\u7684\u6307\u9488\u3011\u7684\u6570\u7ec4\u5417\uff1f<\/p>\n
int (*a[9])[5];<\/pre>\n
\u4f60\u4f1a\u58f0\u660e\u6307\u5411\u3010\u6307\u9488\u7684\u6570\u7ec4\u3011\u7684\u6307\u9488\u5417\uff1f<\/p>\n
int *(*a)[5];<\/pre>\n
\u8ba9\u6211\u4eec\u6765\u8bd5\u7740\u9a8c\u8bc1\u4e00\u4e0b\u3002\u600e\u4e48\u9a8c\u8bc1\u5462\uff1f\u53ea\u8981\u6309\u7167\u6982\u5ff5\uff08\u6bd4\u5982\u6570\u7ec4\u7684\u6307\u9488\u7684\u6570\u7ec4\uff09\uff0c\u4e00\u6b65\u4e00\u6b65\u6784\u9020\u5e76\u4e14\u8d4b\u503c\uff0c\u6700\u540e\u80fd\u7f16\u8bd1\u901a\u8fc7\uff0c\u6ca1\u6709\u8b66\u544a\uff0c\u5c31\u8bf4\u660e\u6211\u4eec\u4ece\u6982\u5ff5\u5230\u4ee3\u7801\u7684\u7ffb\u8bd1\u662f\u5bf9\u7684\u3002<\/p>\n
int a1 = 1;\r\nint a2 = 2;\r\nint a3 = 3;\r\nint a4 = 4;\r\nint a5 = 5;\r\n\r\nint aa1[5] = {1, 2, 3, 4, 5};\r\nint aa2[5] = {1, 2, 3, 4, 5};\r\nint aa3[5] = {1, 2, 3, 4, 5};\r\n\/\/ \u4e8c\u7ef4\r\nint *aa[5] = {&a1, &a2, &a3, &a4, &a5};\r\nint (*aa1d)[5] = &aa1;\r\n\/\/ \u4e09\u7ef4\r\nint *(*a)[5] = &aa;\r\nint (*b[3])[5] = {&aa1, &aa2, &aa3};<\/pre>\n
\u770b\u660e\u767d\u4e86\u5417\uff1f\u8fd9\u80cc\u540e\u7684\u539f\u7406\u662f\u4ec0\u4e48\u5462\uff1f<\/p>\n
\u5b9e\u9645\u4e0a\u8fd9\u4f53\u73b0\u4e86\u67d0\u79cd\u9012\u5f52\u6027\u2014\u2014<\/p>\n
\u5982\u679c\u4e00\u4e2a\u58f0\u660e\u5f62\u5982 T *D\uff08\u5047\u8bbe\u53d8\u91cf ident \u5728 D \u4e2d\uff09\uff0c\u800c T D \u58f0\u660e\u4e86\u4e00\u4e2a\u3010\u5b9a\u8bed + T\u3011\u7c7b\u578b\u7684\u53d8\u91cf\u7684\u8bdd\uff0c\u90a3\u4e48 T *D \u5c31\u58f0\u660e\u4e86\u6307\u5411\u7c7b\u578b T \u7684\u3010\u5b9a\u8bed + \u6307\u9488\u3011 ident\u3002
\n\u5982\u679c\u4e00\u4e2a\u58f0\u660e\u5f62\u5982 T D[n]\uff08\u5047\u8bbe\u53d8\u91cf ident \u5728 D \u4e2d\uff09\uff0c\u800c T D \u58f0\u660e\u4e86\u4e00\u4e2a\u3010\u5b9a\u8bed + T\u3011\u7c7b\u578b\u7684\u53d8\u91cf\u7684\u8bdd\uff0c\u90a3\u4e48 T D[n] \u5c31\u58f0\u660e\u4e86\u957f\u5ea6\u4e3a n \u7684\u3001\u7c7b\u578b\u4e3a T \u7684\u3010\u5b9a\u8bed + \u6570\u7ec4\u3011ident\u3002<\/p><\/blockquote>\n
\u6709\u4e9b\u6666\u6da9\uff0c\u662f\u4e0d\u662f\uff1f\u8ba9\u6211\u4eec\u518d\u62ff\u4f8b\u5b50\u56de\u987e\u4e00\u4e0b\u3002\u6bd4\u5982 int (*b[3])[5] \u4e2d\uff1a<\/p>\n