Flex yy_scan_string 内存泄漏
Flex yy_scan_string memory leaks
描述
创建此示例是为了从更大的解决方案中引入问题。我必须使用 flex 和 yy_scan_string()。我在 flex 中遇到内存泄漏问题（下面的代码）。在此示例中，内存泄漏被标记为 "still reachable"，但在原始解决方案中，它们被标记为 "lost memory".
我认为这个问题是在 flex 内部分配的内存中的某个地方，我不知道如何正确释放它，我找不到关于该问题的任何教程/文档。
file.lex
%option noyywrap
%{
#include <stdio.h>
%}
%%
. printf("%s\n", yytext);
%%
int main() {
printf("Start\n");
yy_scan_string("ABC");
yylex();
printf("Stop\n");
return 0;
}
bash$ flex file.lex
bash$ gcc lex.yy.c
bash$ ./a.out
Start
H
a
l
l
o
W
o
r
l
d
Stop
bash$ valgrind --leak-check=full --show-leak-kinds=all ./a.out
==6351== Memcheck, a memory error detector
==6351== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==6351== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==6351== Command: ./a.out
==6351==
==6351== error calling PR_SET_PTRACER, vgdb might block
Start
A
B
C
Stop
==6351==
==6351== HEAP SUMMARY:
==6351== in use at exit: 77 bytes in 3 blocks
==6351== total heap usage: 4 allocs, 1 frees, 589 bytes allocated
==6351==
==6351== 5 bytes in 1 blocks are still reachable in loss record 1 of 3
==6351== at 0x483577F: malloc (vg_replace_malloc.c:299)
==6351== by 0x10AE84: yyalloc (in ./a.out)
==6351== by 0x10ABE5: yy_scan_bytes (in ./a.out)
==6351== by 0x10ABBC: yy_scan_string (in ./a.out)
==6351== by 0x10AEE2: main (in /home/./a.out)
==6351==
==6351== 8 bytes in 1 blocks are still reachable in loss record 2 of 3
==6351== at 0x483577F: malloc (vg_replace_malloc.c:299)
==6351== by 0x10AE84: yyalloc (in ./a.out)
==6351== by 0x10A991: yyensure_buffer_stack (in ./a.out)
==6351== by 0x10A38D: yy_switch_to_buffer (in ./a.out)
==6351== by 0x10AB8E: yy_scan_buffer (in ./a.out)
==6351== by 0x10AC68: yy_scan_bytes (in ./a.out)
==6351== by 0x10ABBC: yy_scan_string (in ./a.out)
==6351== by 0x10AEE2: main (in ./a.out)
==6351==
==6351== 64 bytes in 1 blocks are still reachable in loss record 3 of 3
==6351== at 0x483577F: malloc (vg_replace_malloc.c:299)
==6351== by 0x10AE84: yyalloc (in ./a.out)
==6351== by 0x10AAEF: yy_scan_buffer (in ./a.out)
==6351== by 0x10AC68: yy_scan_bytes (in ./a.out)
==6351== by 0x10ABBC: yy_scan_string (in ./a.out)
==6351== by 0x10AEE2: main (in ./a.out)
==6351==
==6351== LEAK SUMMARY:
==6351== definitely lost: 0 bytes in 0 blocks
==6351== indirectly lost: 0 bytes in 0 blocks
==6351== possibly lost: 0 bytes in 0 blocks
==6351== still reachable: 77 bytes in 3 blocks
==6351== suppressed: 0 bytes in 0 blocks
==6351==
==6351== For counts of detected and suppressed errors, rerun with: -v
==6351== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
答案在flex文档中有提到，但是你得仔细阅读才能找到。 （见下文。）
如果生成可重入扫描器，则您负责创建和销毁所需的每个扫描器对象，并且扫描器对象管理扫描器实例所需的所有内存。但是即使不使用可重入接口，也可以使用yylex_destroy来管理内存。在传统的不可重入接口中，则没有scanner_t参数，所以yylex_destroy的原型就是
int yylex_destroy(void);
（虽然它有一个 return 应该是状态代码的值，但它永远不会 return 出错。）
如果你愿意，你可以调用yylex_init，它在非可重入接口中也没有参数，但与可重入接口不同，没有必要调用它。
来自 memory management 上的手册章节：
Flex allocates dynamic memory during initialization, and once in a while from within a call to yylex(). Initialization takes place during the first call to yylex(). Thereafter, flex may reallocate more memory if it needs to enlarge a buffer. As of version 2.5.9 Flex will clean up all memory when you call yylex_destroy See faq-memory-leak.
示例：
$ cat clean.l
%option noinput nounput noyywrap nodefault
%{
#include <stdio.h>
%}
%%
.|\n ECHO;
%%
int main() {
printf("Start\n");
yy_scan_string("ABC");
yylex();
printf("Stop\n");
yylex_destroy();
return 0;
}
$ flex -o clean.c clean.l
$ gcc -Wall -o clean clean.c
$ valgrind --leak-check=full --show-leak-kinds=all ./clean
==16187== Memcheck, a memory error detector
==16187== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==16187== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==16187== Command: ./clean
==16187==
Start
ABCStop
==16187==
==16187== HEAP SUMMARY:
==16187== in use at exit: 0 bytes in 0 blocks
==16187== total heap usage: 4 allocs, 4 frees, 1,101 bytes allocated
==16187==
==16187== All heap blocks were freed -- no leaks are possible
==16187==
==16187== For counts of detected and suppressed errors, rerun with: -v
==16187== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
描述
创建此示例是为了从更大的解决方案中引入问题。我必须使用 flex 和 yy_scan_string()。我在 flex 中遇到内存泄漏问题（下面的代码）。在此示例中，内存泄漏被标记为 "still reachable"，但在原始解决方案中，它们被标记为 "lost memory".
我认为这个问题是在 flex 内部分配的内存中的某个地方，我不知道如何正确释放它，我找不到关于该问题的任何教程/文档。
file.lex
%option noyywrap
%{
#include <stdio.h>
%}
%%
. printf("%s\n", yytext);
%%
int main() {
printf("Start\n");
yy_scan_string("ABC");
yylex();
printf("Stop\n");
return 0;
}
bash$ flex file.lex
bash$ gcc lex.yy.c
bash$ ./a.out
Start
H
a
l
l
o
W
o
r
l
d
Stop
bash$ valgrind --leak-check=full --show-leak-kinds=all ./a.out
==6351== Memcheck, a memory error detector
==6351== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==6351== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==6351== Command: ./a.out
==6351==
==6351== error calling PR_SET_PTRACER, vgdb might block
Start
A
B
C
Stop
==6351==
==6351== HEAP SUMMARY:
==6351== in use at exit: 77 bytes in 3 blocks
==6351== total heap usage: 4 allocs, 1 frees, 589 bytes allocated
==6351==
==6351== 5 bytes in 1 blocks are still reachable in loss record 1 of 3
==6351== at 0x483577F: malloc (vg_replace_malloc.c:299)
==6351== by 0x10AE84: yyalloc (in ./a.out)
==6351== by 0x10ABE5: yy_scan_bytes (in ./a.out)
==6351== by 0x10ABBC: yy_scan_string (in ./a.out)
==6351== by 0x10AEE2: main (in /home/./a.out)
==6351==
==6351== 8 bytes in 1 blocks are still reachable in loss record 2 of 3
==6351== at 0x483577F: malloc (vg_replace_malloc.c:299)
==6351== by 0x10AE84: yyalloc (in ./a.out)
==6351== by 0x10A991: yyensure_buffer_stack (in ./a.out)
==6351== by 0x10A38D: yy_switch_to_buffer (in ./a.out)
==6351== by 0x10AB8E: yy_scan_buffer (in ./a.out)
==6351== by 0x10AC68: yy_scan_bytes (in ./a.out)
==6351== by 0x10ABBC: yy_scan_string (in ./a.out)
==6351== by 0x10AEE2: main (in ./a.out)
==6351==
==6351== 64 bytes in 1 blocks are still reachable in loss record 3 of 3
==6351== at 0x483577F: malloc (vg_replace_malloc.c:299)
==6351== by 0x10AE84: yyalloc (in ./a.out)
==6351== by 0x10AAEF: yy_scan_buffer (in ./a.out)
==6351== by 0x10AC68: yy_scan_bytes (in ./a.out)
==6351== by 0x10ABBC: yy_scan_string (in ./a.out)
==6351== by 0x10AEE2: main (in ./a.out)
==6351==
==6351== LEAK SUMMARY:
==6351== definitely lost: 0 bytes in 0 blocks
==6351== indirectly lost: 0 bytes in 0 blocks
==6351== possibly lost: 0 bytes in 0 blocks
==6351== still reachable: 77 bytes in 3 blocks
==6351== suppressed: 0 bytes in 0 blocks
==6351==
==6351== For counts of detected and suppressed errors, rerun with: -v
==6351== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
答案在flex文档中有提到，但是你得仔细阅读才能找到。 （见下文。）
如果生成可重入扫描器，则您负责创建和销毁所需的每个扫描器对象，并且扫描器对象管理扫描器实例所需的所有内存。但是即使不使用可重入接口，也可以使用yylex_destroy来管理内存。在传统的不可重入接口中，则没有scanner_t参数，所以yylex_destroy的原型就是
int yylex_destroy(void);
（虽然它有一个 return 应该是状态代码的值，但它永远不会 return 出错。）
如果你愿意，你可以调用yylex_init，它在非可重入接口中也没有参数，但与可重入接口不同，没有必要调用它。
来自 memory management 上的手册章节：
Flex allocates dynamic memory during initialization, and once in a while from within a call to yylex(). Initialization takes place during the first call to yylex(). Thereafter, flex may reallocate more memory if it needs to enlarge a buffer. As of version 2.5.9 Flex will clean up all memory when you call yylex_destroy See faq-memory-leak.
示例：
$ cat clean.l
%option noinput nounput noyywrap nodefault
%{
#include <stdio.h>
%}
%%
.|\n ECHO;
%%
int main() {
printf("Start\n");
yy_scan_string("ABC");
yylex();
printf("Stop\n");
yylex_destroy();
return 0;
}
$ flex -o clean.c clean.l
$ gcc -Wall -o clean clean.c
$ valgrind --leak-check=full --show-leak-kinds=all ./clean
==16187== Memcheck, a memory error detector
==16187== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==16187== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==16187== Command: ./clean
==16187==
Start
ABCStop
==16187==
==16187== HEAP SUMMARY:
==16187== in use at exit: 0 bytes in 0 blocks
==16187== total heap usage: 4 allocs, 4 frees, 1,101 bytes allocated
==16187==
==16187== All heap blocks were freed -- no leaks are possible
==16187==
==16187== For counts of detected and suppressed errors, rerun with: -v
==16187== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)