{"id":3319,"date":"2017-06-02T22:10:26","date_gmt":"2017-06-02T14:10:26","guid":{"rendered":"https:\/\/ixyzero.com\/blog\/?p=3319"},"modified":"2017-06-02T22:10:26","modified_gmt":"2017-06-02T14:10:26","slug":"c%e8%af%ad%e8%a8%80%e4%b8%ad%e7%9a%84sizeof%e5%92%8cmalloc","status":"publish","type":"post","link":"https:\/\/ixyzero.com\/blog\/archives\/3319.html","title":{"rendered":"C\u8bed\u8a00\u4e2d\u7684sizeof\u548cmalloc"},"content":{"rendered":"

=Start=<\/p>\n

\u7f18\u7531\uff1a<\/h4>\n

\u6700\u8fd1\u5728\u7528C\u8bed\u8a00\u5199\u7a0b\u5e8f\uff0c\u7531\u4e8eC\u8bed\u8a00\u7684\u57fa\u7840\u5df2\u7ecf\u5fd8\u5f97\u5dee\u4e0d\u591a\u4e86\uff08\u4e5f\u53ef\u80fd\u662f\u4e4b\u524d\u5c31\u6ca1\u5b66\u597d\u2026\u2026\uff09\uff0c\u5728\u5b9e\u73b0\u4e00\u4e2a\u7b80\u5355\u7684\u529f\u80fd\u65f6\u5c31\u78b0\u5230\u4e86\u597d\u591a\u95ee\u9898\uff0c\u5728\u8fd9\u91cc\u5c31\u8bb0\u5f55\u4e00\u4e0b\u5176\u4e2d\u6bd4\u8f83\u5178\u578b\u7684\u548csizeof\u548cmalloc\u76f8\u5173\u7684\u95ee\u9898\uff08\u611f\u89c9\u7528\u8fd9\u79cd\u63a5\u8fd1\u4e8e\u5b9e\u6218\u7684\u7f16\u7a0b\u9898\u53bb\u9762\u8bd5\u5019\u9009\u8005\uff0c\u6548\u679c\u4f1a\u5f88\u597d\uff0c^_^\uff09<\/p>\n

\u6b63\u6587\uff1a<\/h4>\n

\u53c2\u8003\u89e3\u7b54\uff1a<\/h5>\n

sizeof\u662fC\u8bed\u8a00\u7684\u4e00\u79cd\u5355\u76ee\u64cd\u4f5c\u7b26<\/strong><\/span>\uff0c\u5982C\u8bed\u8a00\u7684\u5176\u4ed6\u64cd\u4f5c\u7b26++\u3001\u2013\u7b49\u3002\u5b83\u5e76\u4e0d\u662f\u51fd\u6570\u3002sizeof\u64cd\u4f5c\u7b26\u4ee5\u5b57\u8282\u5f62\u5f0f\u7ed9\u51fa\u4e86\u5176\u64cd\u4f5c\u6570\u7684\u5b58\u50a8\u5927\u5c0f\u3002\u64cd\u4f5c\u6570\u53ef\u4ee5\u662f\u4e00\u4e2a\u8868\u8fbe\u5f0f\u6216\u62ec\u5728\u62ec\u53f7\u5185\u7684\u7c7b\u578b\u540d\u3002\u64cd\u4f5c\u6570\u7684\u5b58\u50a8\u5927\u5c0f\u7531\u64cd\u4f5c\u6570\u7684\u7c7b\u578b\u51b3\u5b9a\u3002<\/p>\n

\n<\/blockquote>\n

void *malloc(size_t size);
\nvoid free(void *ptr);<\/p>\n

The malloc() function allocates size bytes and returns a pointer to the allocated memory. The memory is not initialized.<\/strong><\/span> If size is 0, then malloc() returns either NULL, or a unique pointer value that can later be successfully passed to free().<\/p>\n

The free() function frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc<\/strong>(), calloc<\/strong>() or realloc<\/strong>().<\/span> Otherwise, or if free(ptr) has already been called before, undefined behavior occurs. If ptr is NULL, no operation is performed.<\/strong><\/span><\/p><\/blockquote>\n

\u5728\u4e0b\u9762\u7684\u4e00\u6bb5\u4ee3\u7801\u4e2d\u5b58\u5728\u51e0\u4e2a\u9519\u8bef\u548c\u51e0\u4e2a\u4e0d\u592a\u5408\u7406\u7684\u5730\u65b9\uff0c\u8bf7\u627e\u51fa\u6765\u5e76\u8bf4\u660e\u539f\u56e0\uff1a<\/p>\n

\n
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\n\n\n\n
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#include <stdio.h><\/code><\/div>\n
#include <stdlib.h><\/code><\/div>\n
#include <time.h><\/code><\/div>\n
<\/div>\n
char<\/code> *get_current_time(<\/code>const<\/code> char<\/code>* format) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>time_t t;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>struct tm *tmp;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>t = time(NULL);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>tmp = localtime(&t);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (tmp == NULL) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>perror(<\/code>\"localtime\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> NULL;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>char<\/code> *outstr = (<\/code>char<\/code> *) malloc(sizeof(<\/code>char<\/code>) * <\/code>128<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (outstr == NULL) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>perror(<\/code>\"malloc\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> NULL;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (strftime(outstr, sizeof(outstr), format, tmp) == <\/code>0<\/code>) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>fprintf(stderr, <\/code>\"strftime returned 0\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> NULL;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>printf(<\/code>\"Result string is \\\"%s\\\"\\n\"<\/code>, outstr);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> outstr;<\/code><\/div>\n
}<\/code><\/div>\n
<\/div>\n
int<\/code> main(<\/code>int<\/code> argc, <\/code>char<\/code> const<\/code> *argv[]) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>char<\/code> *time_str;<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (argc == <\/code>2<\/code>) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>time_str = get_current_time(argv[<\/code>1<\/code>]);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>} <\/code>else<\/code> {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>time_str = get_current_time(<\/code>\"%F %T\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>printf(<\/code>\"%s\\n\"<\/code>, time_str);<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> 0<\/code>;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\u9519\u8bef1\u3001\u5728get_current_time\u51fd\u6570\u91cc\uff1a<\/h6>\n
\n
\n
\n
\n\n\n\n
\n
\n
char<\/code> *get_current_time(<\/code>const<\/code> char<\/code>* format) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>time_t t;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>struct tm *tmp;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>t = time(NULL);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>tmp = localtime(&t);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (tmp == NULL) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>perror(<\/code>\"localtime\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> NULL;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>char<\/code> *outstr = (<\/code>char<\/code> *) malloc(sizeof(<\/code>char<\/code>) * <\/code>128<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (outstr == NULL) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>perror(<\/code>\"malloc\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> NULL;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/ if (strftime(outstr, sizeof(outstr), format, tmp) == 0) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/*<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>strftime returned 0<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>Segmentation fault (core dumped)<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\u95ee\u9898\u51fa\u5728sizeof\u7684\u4f7f\u7528\u4e0a\uff0c\u56e0\u4e3aoutstr\u53ea\u662f\u4e00\u4e2a(char *)\u7c7b\u578b\u7684\u6307\u9488\uff0c\u6240\u4ee5sizeof(outstr)==4<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\u800c\u6211\u4eec\u7684\u9700\u6c42\u5b9e\u9645\u4e0a\u662f\u83b7\u53d6outstr\u6307\u5411\u5185\u5bb9\u88ab\u5206\u914d\u5230\u7684\u957f\u5ea6\u5927\u5c0f\uff0c\u6ca1\u529e\u6cd5\u901a\u8fc7sizeof\u6765\u83b7\u53d6\uff0c\u6700\u597d\u662f\u81ea\u5df1\u5728malloc\u65f6\u8bb0\u5f55\u4e00\u4e0b<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>*\/<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (strftime(outstr, <\/code>128<\/code>, format, tmp) == <\/code>0<\/code>) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>fprintf(stderr, <\/code>\"strftime returned 0\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> NULL;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>printf(<\/code>\"Result string is \\\"%s\\\"\\n\"<\/code>, outstr);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> outstr;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\u9519\u8bef2\u3001\u5728main\u51fd\u6570\u91cc\uff1a<\/h6>\n
\n
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\n\n\n\n
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int<\/code> main(<\/code>int<\/code> argc, <\/code>char<\/code> const<\/code> *argv[]) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>char<\/code> *time_str;<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (argc == <\/code>2<\/code>) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>time_str = get_current_time(argv[<\/code>1<\/code>]);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>} <\/code>else<\/code> {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>time_str = get_current_time(<\/code>\"%F %T\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>printf(<\/code>\"%s\\n\"<\/code>, time_str);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/*<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\u56e0\u4e3a get_current_time \u8fd4\u56de\u7684\u662f\u6307\u5411 malloc \u5206\u914d\u7a7a\u95f4\u7684\u6307\u9488\uff0c<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\u6240\u4ee5\u5728\u4f7f\u7528\u5b8c\u4e86\u4e4b\u540e\u9700\u8981\u624b\u52a8\u663e\u793a free \uff0c\u907f\u514d\u5185\u5b58\u6cc4\u9732\u7684\u95ee\u9898\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>*\/<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>free(time_str);<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> 0<\/code>;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\u53c2\u8003\u94fe\u63a5\uff1a<\/h5>\n