004 變數使用前記得初始化; 回家作業參考解答

上週習題

• 除了手動測試外,有沒有更聰明一點的方式,可以幫你找到程式碼中,未看先猜未初始化就使用的可能錯誤?

參考解答

==22043== Conditional jump or move depends on uninitialised value(s)

==22043==    at 0x539AF90: vfprintf (vfprintf.c:1655)

==22043==    by 0x53A1FF8: printf (printf.c:34)

==22043==    by 0x400982: bar() (main.cpp:33)

==22043==    by 0x400A1C: main (main.cpp:48)

==22043== 

==22043== Use of uninitialised value of size 8

==22043==    at 0x5397551: _itoa_word (_itoa.c:180)

==22043==    by 0x539BAE1: vfprintf (vfprintf.c:1654)

==22043==    by 0x53A1FF8: printf (printf.c:34)

==22043==    by 0x4009B6: bar() (main.cpp:38)

==22043==    by 0x400A1C: main (main.cpp:48)

==22043== 

==22043== HEAP SUMMARY:

==22043==     in use at exit: 0 bytes in 0 blocks

==22043==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated

==22043== 

==22043== All heap blocks were freed -- no leaks are possible

==22043== 

==22043== For counts of detected and suppressed errors, rerun with: -v

==22043== Use --track-origins=yes to see where uninitialised values come from

==22043== ERROR SUMMARY: 109 errors from 15 contexts (suppressed: 0 from 0)

參考工具（廣為人知，但也很多人選擇不用的）

http://valgrind.org/