我无法破译我正在获得的Valgrind输出。例如，我有一个错误，说我正在进行大小为1的非法写入。所以我在malloc中添加了一个并没有改变任何东西。由于我之前从未使用过Valgrind，我认为最好在网上搜索后得到一些帮助，但没有得到回复。请注意，我不是在寻找答案，所以我没有复制我的代码。我希望被推向正确的方向，以便我能够对抗未来的错误。 谢谢！
==28881== Memcheck, a memory error detector
==28881== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==28881== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==28881== Command: ./sws root
==28881==
==28892== Conditional jump or move depends on uninitialised value(s)
==28892== at 0x4C286D9: __GI_strlen (mc_replace_strmem.c:284)
==28892== by 0x4040B7: get_headers (html.c:280)
==28892== by 0x402D77: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Conditional jump or move depends on uninitialised value(s)
==28892== at 0x4C286D9: __GI_strlen (mc_replace_strmem.c:284)
==28892== by 0x4040C5: get_headers (html.c:280)
==28892== by 0x402D77: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Conditional jump or move depends on uninitialised value(s)
==28892== at 0x4C286D9: __GI_strlen (mc_replace_strmem.c:284)
==28892== by 0x4040D3: get_headers (html.c:280)
==28892== by 0x402D77: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Conditional jump or move depends on uninitialised value(s)
==28892== at 0x4C286D9: __GI_strlen (mc_replace_strmem.c:284)
==28892== by 0x4040E1: get_headers (html.c:280)
==28892== by 0x402D77: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid write of size 1
==28892== at 0x4C2874C: strcpy (mc_replace_strmem.c:311)
==28892== by 0x4041E1: get_headers (html.c:299)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid write of size 1
==28892== at 0x4C2875F: strcpy (mc_replace_strmem.c:311)
==28892== by 0x4041E1: get_headers (html.c:299)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be034 is 4 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid read of size 1
==28892== at 0x4C28374: strcat (mc_replace_strmem.c:176)
==28892== by 0x4041F7: get_headers (html.c:300)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid write of size 1
==28892== at 0x4C2838C: strcat (mc_replace_strmem.c:176)
==28892== by 0x4041F7: get_headers (html.c:300)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be034 is 4 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid write of size 1
==28892== at 0x4C2839F: strcat (mc_replace_strmem.c:176)
==28892== by 0x4041F7: get_headers (html.c:300)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be061 is 15 bytes before a block of size 40 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x403E53: get_headers (html.c:224)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid read of size 1
==28892== at 0x4C28374: strcat (mc_replace_strmem.c:176)
==28892== by 0x40420D: get_headers (html.c:301)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== Invalid read of size 1
==28892== at 0x4C28374: strcat (mc_replace_strmem.c:176)
==28892== by 0x40420D: get_headers (html.c:301)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid write of size 1
==28892== at 0x4C2838C: strcat (mc_replace_strmem.c:176)
==28892== by 0x40420D: get_headers (html.c:301)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be061 is 15 bytes before a block of size 40 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x403E53: get_headers (html.c:224)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid read of size 1
==28892== at 0x4C28374: strcat (mc_replace_strmem.c:176)
==28892== by 0x404223: get_headers (html.c:302)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid read of size 1
==28892== at 0x4C28374: strcat (mc_replace_strmem.c:176)
==28892== by 0x404239: get_headers (html.c:303)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid write of size 1
==28892== at 0x4C2838C: strcat (mc_replace_strmem.c:176)
==28892== by 0x404239: get_headers (html.c:303)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be098 is 0 bytes after a block of size 40 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x403E53: get_headers (html.c:224)
==28892== by 0x402E00: read_page (networking.c:347)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Invalid read of size 1
==28892== at 0x4C286E4: __GI_strlen (mc_replace_strmem.c:284)
==28892== by 0x402E0F: read_page (networking.c:348)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892== Syscall param socketcall.sendto(msg) points to unaddressable byte(s)
==28892== at 0x5121052: send (send.c:28)
==28892== by 0x40276D: send_msg (networking.c:245)
==28892== by 0x402E29: read_page (networking.c:348)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892== Address 0x53be030 is 0 bytes after a block of size 32 alloc'd
==28892== at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==28892== by 0x402D84: read_page (networking.c:341)
==28892== by 0x402B8E: get_page (networking.c:310)
==28892== by 0x40268E: header_parse (networking.c:232)
==28892== by 0x401D96: retrieve_msg (networking.c:62)
==28892== by 0x401AAB: main (sws.c:139)
==28892==
==28892==
==28892== HEAP SUMMARY:
==28892== in use at exit: 337 bytes in 10 blocks
==28892== total heap usage: 19 allocs, 9 frees, 3,307 bytes allocated
==28892==
==28892== LEAK SUMMARY:
==28892== definitely lost: 337 bytes in 10 blocks
==28892== indirectly lost: 0 bytes in 0 blocks
==28892== possibly lost: 0 bytes in 0 blocks
==28892== still reachable: 0 bytes in 0 blocks
==28892== suppressed: 0 bytes in 0 blocks
==28892== Rerun with --leak-check=full to see details of leaked memory
==28892==
==28892== For counts of detected and suppressed errors, rerun with: -v
==28892== Use --track-origins=yes to see where uninitialised values come from
==28892== ERROR SUMMARY: 348 errors from 17 contexts (suppressed: 4 from 4)
==28881==
==28881== HEAP SUMMARY:
==28881== in use at exit: 0 bytes in 0 blocks
==28881== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==28881==
==28881== All heap blocks were freed -- no leaks are possible
==28881==
==28881== For counts of detected and suppressed errors, rerun with: -v
==28881== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 4)
217 int get_headers(char* time, char* last_modified, char* server, char* content_type, size_t msglen, char* header, int flag)
218 {
219 char* header1 = NULL;
220 char* header2 = NULL;
221 char* header3 = NULL;
222 char* header4 = NULL;
223 char* header5 = NULL;
224
225 if ((header1 = (char*)malloc(strlen("Date: ")+strlen(time)+2) ) ==NULL)
226 {
227 fprintf(stderr, "%s: No more memory\n", getprogname());
228 exit(EXIT_FAILURE);
229 }
230
231
232 strcpy(header1, "Date: ");
233 strcat(header1, time);
234 strcat(header1, "\n");
235
236
237 if ((header2 = (char*)malloc(strlen("Last-Modified: ")+strlen(last_modified)+5) ) ==NULL)
238 {
239 fprintf(stderr, "%s: No more memory\n", getprogname());
240 exit(EXIT_FAILURE);
241 }
242
243
244 strcpy(header2, "Last-Modified: ");
245 strcat(header2, last_modified);
246 strcat(header2, "\n");
247
248
249 if ((header3 = (char*)malloc(strlen("Server: ")+strlen(server)+5) ) ==NULL)
250 {
251 fprintf(stderr, "%s: No more memory\n", getprogname());
252 exit(EXIT_FAILURE);
253 }
254
255
256 strcpy(header3, "Server: ");
257 strcat(header3, server);
258 strcat(header3, "\n");
259
260
261 if ((header4 = (char*)malloc(strlen("Content-Type: ")+strlen(content_type)+5) ) ==NULL)
262 {
263 fprintf(stderr, "%s: No more memory\n", getprogname());
264 exit(EXIT_FAILURE);
265 }
266
267
268 strcpy(header4, "Content-Type: ");
269 strcat(header4, content_type);
270 strcat(header4, "\n");
271
272
273 int content_length = strlen(header1)+strlen(header2)+strlen(header3)+strlen(header4)+strlen("Content-Length: ")+msglen+5;
274 char temp[10] = {' '};
275 snprintf(temp, sizeof(msglen),"%d", content_length);
276
277 if ((header5 = (char*)malloc(strlen("Content-Length: ")+strlen(temp)+5) ) ==NULL)
278 {
279 fprintf(stderr, "%s: No more memory\n", getprogname());
280 exit(EXIT_FAILURE);
281 }
282
283
284 strcpy(header5, "Content-Length: ");
285 strncat(header5, temp, strlen(temp));
286 strcat(header5, "\n\n");
287
288
289 if(flag == 1)
290 {
291 strcpy(header, header1);
292 strcat(header, header2);
293 strcat(header, header3);
294 strcat(header, header4);
295 strcat(header, header5);
296 }
297
298 return content_length;
299 free(header1);
300 free(header2);
301 free(header3);
302 free(header4);
303 free(header5);
304 }
答案 0 :(得分：3)
如果flag为0，那么您永远不会初始化header1..4字符串中的任何数据，因此当您尝试使用strlen获取其长度时，您会读入未初始化的垃圾。无论flag设置如何，您都应确保始终将标头值初始化为空字符串。
此外，没有必要strcat(..., "\0")到字符串 - strcpy和strcat总是空终止字符串（实际上，"\0"与空字符无法区分字符串""，因为它们的第一个字节都是NUL字节）。在将一堆字符串连接在一起时要小心Shlemiel the Painter algorithms。
答案 1 :(得分：1)
1）你malloc'd 5件内存并没有在你的功能中释放它们。这些应在您返回或退出之前释放。注意valgrind如何说你有326个字节是definitely lost。
2）如果flag为假，你的header*变量永远不会被设置为任何东西，这就是为什么valgrind在第280行给你一堆错误的原因。随后，它没有任何好处。稍后在第301行复制，这样你就会得到更多错误。
答案 2 :(得分：1)
由于您有兴趣编写“整洁+酷”代码，我将尝试将您推向正确的方向。防范未来错误的最佳方法是保持简单。
什么是简单的？尽可能少地使用它，但仍然保持可读性和易于理解。代替87行（304-217）的代码，你可以用30行代码完成。
此外，了解代码可能会进入“未定义”行为的地方是一种良好的心态。最好在get_header（）中包含标题的大小。如果它在get_header（）中不可用，则无法防止潜在的缓冲区溢出/内存损坏。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
get_header(char *date, char *last_m, char *server, char *c_type,
int c_len, char *header, int flag, int h_len);
int
main()
{
char header[500];
int n;
n = get_header(
"Fri, 09 Nov 2012 09:22:06 GMT", /* Date */
"Fri, 09 Nov 2012 09:10:32 GMT", /* Last modified */
"MySuperDuperServer/V 1.0.0.0", /* Server name */
"Text/html", /* Content type */
1234, /* Content length */
header, /* Destination buf */
1, /* 1 = write into header, 0 = Do not */
sizeof(header) /* header buf size */
);
printf("%s\n", header);
exit(0);
}
/* Header lines should end with CR LF */
#define DATE "Date: %s\r\n"
#define LAST_M "Last-Modified: %s\r\n"
#define SERVER "Server : %s\r\n"
#define C_TYPE "Content-Type: %s\r\n"
#define C_LEN "Content-Length: %d\r\n\r\n"
#define HEADER DATE LAST_M SERVER C_TYPE C_LEN
int
get_header(char *date, char *last_m, char *server, char *c_type,
int c_len, char *header, int flag, int h_len)
{
char *d;
int r;
if (flag == 1) {
d = header;
}
else if ((d = (char *)malloc(h_len)) == 0) {
printf("out of memory\n");
exit(1); /* exit(EXIT_FAILURE); */
}
r = snprintf(d, h_len, HEADER, date, last_m, server, c_type, c_len);
if (flag == 0) {
free(d);
}
return(r);
}
我希望你觉得这很有用。