Pointer changes value at an unexpected place
In an attempt to debug this problem, I have added printf statements to see what is happening when the code is running.
The printf statement containing “#103D” gives a good value for “FirstPtr” but then its value changes.
I am using Borland C++ IDE to write 16 bit code for a picoFlash single board computer with a 186 compatible processor and 512K of Ram. I am adding code to an existing program that takes 183 pages to print. I have checked the “check stack overflow” option. The compiler and linker don’t give any error messages.
I don’t know what other information I should inclue because I have no idea what is happening.
How can I get to the bottom of this problem?
Code:void DownloadAFile(char *strDirectory,char *strFileName,char *strRxBlock, int intOffset) { char *FirstPtr; //Pointer used to parse the incomming Request char strNrChars[4]; //Number of characters to follow int intNrChars; //Number of characters following next int intLen; //Length of string char strLength[4]; // 4 char string length char *SPtr; //Pointer to the Line Input String static char strLineInput[1024]; //String used for input char *RspPtr; //Pointer to strResponseString static char strResponseString[120]; char *ShortRspPtr; char strShortResponseString[120]; //Without Rec # char strCommandString[100]; char strFullFileName[80]; static char strOldFullFileName[80]; char strRecordNumber[4]; //Requested Record Number int intRecordNumber; //Requested Record Number int intSameFileFlag; static FILE *TxtDLFilePtr; char strTmpStr[80]; static int intLastRecordRead; int intLastRecordReadPlus1; int intContinueRecs; //1 => Continue reading records int intBlockNr; char strRecNr[4]; //Skip code here //Pick intRecordNumber FirstPtr = &strRxBlock[0]; //to 1 printf("#103 ok not term strRxBlock = %s\n", FirstPtr); //ok printf("#103B s/b=1 Ptr @ strRxBlock[0] = %p\n", FirstPtr); //ok FirstPtr+= intOffset; //Beginning of # char in Rec # to 29 printf("#103C s/b=29 Ptr @ Nr char in RecordNr = %p\n", FirstPtr); //ok // TempPtr = FirstPtr; strncpy (strNrChars,FirstPtr,4); //Nr chars in Record # ok //The value of FirstPtr printed with the following line is ok = 5E7E:0AE4 printf("#103D after strncpy FirstPtr = %p\n", FirstPtr); //ok strNrChars[4] = '\0'; //The value of FirstPtr printed with the following line has changed = 5E7E:0A00 printf("#103E after strncpy FirstPtr = %p\n", FirstPtr); //ok printf("#104 ok strNrChars in Record Nr = %s\n",strNrChars); //Nr chars in Record # 4 ok printf("#103F after strncpy FirstPtr = %p\n", FirstPtr); //ok intNrChars = atoi(strNrChars); printf("#103G after strncpy FirstPtr = %p\n", FirstPtr); //ok printf("#105 ok intNrChars = %d\n",intNrChars); // = 4 ok printf("#103H after strncpy FirstPtr = %p\n", FirstPtr); //ok //More code follows
