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POVC++ 6.0 access violation when run in debugger
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copied!<p>I am trying to add enhancements to a 4 year old VC++ 6.0 program. The debug build runs from the command line but not in the debugger: it crashes with an access violation inside printf(). If I skip the printf, then it crashes in malloc() (called from within fopen()) and I can't skip over that.</p> <p>This means I cannot run in the debugger and have to rely on the old printf statements to see what's going on. This obviously makes it a lot harder.</p> <p>Any idea why printf() and malloc() would fail when running under the VC++ debugger? I am no good at this low level stuff!</p> <p>Here is the call stack after the access violation:</p> <pre><code>_heap_alloc_dbg(unsigned int 24, int 2, const char * 0x0046b3d8 `string', int 225) line 394 + 8 bytes _nh_malloc_dbg(unsigned int 24, int 0, int 2, const char * 0x0046b3d8 `string', int 225) line 242 + 21 bytes _malloc_dbg(unsigned int 24, int 2, const char * 0x0046b3d8 `string', int 225) line 163 + 27 bytes _lock(int 2) line 225 + 19 bytes _getstream() line 55 + 7 bytes _fsopen(const char * 0x00468000 `string', const char * 0x00466280 `string', int 64) line 61 + 5 bytes fopen(const char * 0x00468000 `string', const char * 0x00466280 `string') line 104 + 15 bytes open_new_log(const char * 0x00468000 `string') line 66 + 14 bytes log_open(const char * 0x00468000 `string', int 0) line 106 + 9 bytes Xlog_open(const char * 0x00468000 `string', int 0) line 51 + 13 bytes service_start(unsigned long 1, char * * 0x009a0e50) line 3152 + 12 bytes service_init2(char * 0x00471fcc char * NTPROGRAM, char * 0x004723c4 char * NTSERVICE, char * 0x00466540 `string', unsigned long 1, char * * 0x009a0e50) line 508 + 13 bytes service_init(char * 0x00471fcc char * NTPROGRAM, char * 0x004723c4 char * NTSERVICE, unsigned long 2, char * * 0x009a0e50) line 548 main(unsigned long 2, char * * 0x009a0e50) line 3131 mainCRTStartup() line 206 + 25 bytes KERNEL32! 7c817067() </code></pre> <p>Here is the debug dissassembly up to the operation that fails:</p> <pre><code>0041EA7E jmp _heap_alloc_dbg+2B3h (0041eb23) 0041EA83 mov edx,dword ptr [_lTotalAlloc (004b4294)] 0041EA89 add edx,dword ptr [nSize] 0041EA8C mov dword ptr [_lTotalAlloc (004b4294)],edx 0041EA92 mov eax,[_lCurAlloc (004b429c)] 0041EA97 add eax,dword ptr [nSize] 0041EA9A mov [_lCurAlloc (004b429c)],eax 0041EA9F mov ecx,dword ptr [_lCurAlloc (004b429c)] 0041EAA5 cmp ecx,dword ptr [_lMaxAlloc (004b42a0)] 0041EAAB jbe _heap_alloc_dbg+249h (0041eab9) 0041EAAD mov edx,dword ptr [_lCurAlloc (004b429c)] 0041EAB3 mov dword ptr [_lMaxAlloc (004b42a0)],edx 0041EAB9 cmp dword ptr [_pFirstBlock (004b4298)],0 0041EAC0 je _heap_alloc_dbg+25Fh (0041eacf) 0041EAC2 mov eax,[_pFirstBlock (004b4298)] 0041EAC7 mov ecx,dword ptr [pHead] 0041EACA mov dword ptr [eax+4],ecx </code></pre> <p>Here is our source for that calls fopen() and fails in malloc()</p> <pre><code>FILE *open_new_log( const char *logfile ) { FILE *fp; int retry = 0; while( ( fp = fopen( logfile, "w" ) ) == NULL && ++retry < 300 ) Sleep( 1000 ); return( fp ); } </code></pre> <p>The error I get is</p> <pre><code>Unhandled exception inPISCOOP.exe: 0xC00000005: Access Violation </code></pre> <p>Regards,</p> <p>--- Alistair.</p>

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