Pointers and String Processing Error

Question

I've been staring at this code for quite awhile and I can't find out what's wrong with this code and how to fix it. I think one of the arrays is being written past whats been allocated.

The debugger is allowing me to compile, but when I do, I get:

Unhandled exception at 0x774615de in HW6_StringProcessing.exe: 0xC0000005: Access violation.

Here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_STR_SIZE 100

void convertToPigLatin (char * strPtr, char * pStrPtr);

int main(int argc, char *argv[])
{
   char str[MAX_STR_SIZE];
   char pStr[MAX_STR_SIZE];
   FILE *fileInPtr;                             //Create file name
   FILE *fileOutPtr;    

   fileInPtr = fopen("pigLatinIn.txt", "r");    //Assign text to file
   fileOutPtr = fopen("pigLatinOut.txt", "w");

   if(fileInPtr == NULL)                        //Check if file exists
   {
      printf("Failed");
      exit(-1); 
   }
   fprintf(fileOutPtr, "English Word\t\t\t\tPig Latin Word\n");
   fprintf(fileOutPtr, "---------------\t\t\t\t----------------\n");

   while(!feof(fileInPtr))                  //Cycles until end of text
   {

      fscanf(fileInPtr, "%99s", str);       //Assigns word to *char

      str[99] = '\0';                       //Optional: Whole line

      convertToPigLatin(str, pStr); 

      //fprintf(fileOutPtr, "%15s\t\t\t\t%15p\n", str, pStr); 

      printf("%s\n", str); 
   }  

   system("pause"); 
}

void convertToPigLatin (const char * strPtr, char * pStrPtr)
{
   int VowelDetect = 0; 
   int LoopCounter = 0; 
   int consonantCounter = 0; 
   char cStr[MAX_STR_SIZE] = {'\0'};
   char dStr[] = {'-','\0'}; 
   char ayStr[] = {'a','y','\0'};
   char wayStr[] = {'w','a','y','\0'};

   while (*strPtr != '\0')
   {
      if (*strPtr == 'a' || *strPtr == 'e' || 
          *strPtr == 'i' || *strPtr == 'o' || 
          *strPtr == 'u' || VowelDetect ==1)
      {
         strncat(pStrPtr, strPtr, 1); 
         VowelDetect = 1; 
      }
      else
      {
         strncat(cStr, strPtr, 1); 
         consonantCounter++; 
      }
      *strPtr++;
   }
   strcat(pStrPtr, dStr); 
   if (consonantCounter == 0)  
   {
      strcat(pStrPtr, wayStr);
   }
   else
   {
      strcat(cStr,ayStr);
      strcat(pStrPtr, cStr);
   }  
   printf("%s\n", pStrPtr);                         

}

Answer 1

Here's an annotated, working version with some changes and suggestions. You'll probably want to toss the final printf, but I wanted to make sure there was visible output on the first run. The intent here is to stay close to the question's actual code, not to rewrite it entirely.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define XSTR(n) #n // a hack to allow stringify to use the *value of a macro
#define STR(n) XSTR(n)
#define MAX_STR_SIZE 100

void convertToPigLatin (const char * strPtr, char * pStrPtr);

int main(int argc, char *argv[])
{
    // The str and pStr aren't very meaningful, I'd suggent eng and pig.
    // Adding -"Str" to all your strings just slows down reading.
    // - plus it makes "str" an anomaly.
    char str[MAX_STR_SIZE + 1];   // +1 since NUL is usually not counted..
    char pStr[MAX_STR_SIZE + 1];  // ...by functions like strlen().  
    FILE *fileInPtr  = fopen("pigLatinIn.txt", "r");    //Assign text to file
    FILE *fileOutPtr = fopen("pigLatinOut.txt", "w");
    const char *fmt = "%15s     %s\n"; // for head and table output.
    if( ! (fileInPtr && fileOutPtr)) {
        perror("unable to open file(s) for I/O")
        return -1;
    }
    fprintf(fileOutPtr, fmt, "English Word", "Pig Latin Word");
    fprintf(fileOutPtr, fmt, "------------", "---------------");

    // put test before fscanf so we don't lose the last input line on EOF
    while(!feof(fileInPtr))           //Cycles until end of text
    {
        if(1 == fscanf(fileInPtr, "%" STR(MAX_STR_SIZE) "s", str))
        {
            str[MAX_STR_SIZE] = '\0';      //Optional: Whole line
            convertToPigLatin(str, pStr); 
            fprintf(fileOutPtr, fmt, str, pStr);
        }
        // else fprintf(stderr, "skipping empty line\n");  // for example.
    }  
    // system("pause") would be... icky, sleep(...) or 
    // getchar() are better, but still odd since output is going
    // to a file
    fclose(fileInPtr);
    fclose(fileOutPtr);
    return 0;           // a zero exit status from main() means success :-)
}

void convertToPigLatin (const char * strPtr, char * pStrPtr)
{
    int VowelDetected = 0;
    int LoopCounter = 0; 
    int ConsonantCounter = 0; 
    char cStr[MAX_STR_SIZE + 1] = {'\0'};
    char dStr[]   = "-";    // same as {'-','\0'}; 
    char ayStr[]  = "ay";   // same as {'a','y','\0'};
    char wayStr[] = "way";  // same as {'w','a','y','\0'};

    pStrPtr[0] = '\0';      // clear out pStr so trash doesn't prefix output.

    // a better loop control would be:  for( /*prior*/ ; *strPtr ; ++strPtr)
    //  - which lets you move the strPtr++ to the top line of the for loop.
    while (*strPtr != '\0')    // could simplify to:  while(*strPtr)
    {
#if 0   // disabling this to show a different option in the #else clause
        if (   *strPtr == 'a'
            || *strPtr == 'e'
            || *strPtr == 'i'
            || *strPtr == 'o'
            || *strPtr == 'u'
            || VowelDetected == 1)
        {
#else
        if (strchr("aeiou", *strPtr) || VowelDetected == 1)
        {
#endif
            strncat(pStrPtr, strPtr, 1); 
            VowelDetected = 1; 
        }
        else
        {
            strncat(cStr, strPtr, 1); 
            ConsonantCounter++; 
        }
        ++strPtr;   // a *strPtr++ would increment the target char itself.
    }
    strcat(pStrPtr, dStr);
    if (ConsonantCounter == 0)     // or: if( ! Consonantcounter)
    {
        strcat(pStrPtr, wayStr);
    }
    else
    {
        strcat(cStr,ayStr);
        strcat(pStrPtr, cStr);
    }  

    printf("# %s\n", pStrPtr);
}

Answer 2

I think the issue might be the use of strcat() and strncat() to a buffer which hasn't been initialised. Before calling convertToPigLatin(), ensure you blat pStr[] with memset() or some such:

while(!feof(fileInPtr)) {
    ...
    str[99] = '\0';
    pStr[0] = '\0';    // or memset(pStr, 0, sizeof(pStr));
    convertToPigLatin(str, pStr);
    ...
}

Answer 3

Prototype is:

void convertToPigLatin (char * strPtr, char * pStrPtr);

but this function expects const char *

void convertToPigLatin (const char * strPtr, char * pStrPtr)

----------------------------------------^ here

Also, you have to increment the pointer itself (not the value) of strPtr in convertToPigLatin

*strPtr++;

should be:

strPtr++;

Answer 4

The decleration:

void convertToPigLatin (char * strPtr, char * pStrPtr);

is not consistent with the definition of the function:

void convertToPigLatin (const char * strPtr, char * pStrPtr)
{
   ...                       
}