Persistent Segmentation Fault

This is a discussion on Persistent Segmentation Fault within the C Programming forums, part of the General Programming Boards category; I am not certain why the following code I posted causes a persistent segmentation fault when run with one command ...

  1. #1
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    Persistent Segmentation Fault

    I am not certain why the following code I posted causes a persistent segmentation fault when run with one command like argument that is an invalid file name. Please take a look:

    Code:
    else if (argc > 1)	// Command-line arguments greater than one
    	{
    		FILE *inputFile = NULL;
    
    		do
    		{
    
    			while ((inputFile = fopen (*++argv, "r")) == NULL && argc > 1)	// Read arguments until file exists
    			{
    				printf("\n%s\n", *argv);	// Print file name
    				puts("\nFile not found error.\n");
    				argc--;	// Reduce arguments by 1
    			}
    
    
    			if (fgetc(inputFile) == EOF && argc > 1)	// Empty file
    			{
    				printf("\n%s\n", *argv);	// Print the file name
    				printf("\nFile empty.\n");
    			}
    
    			if (argc > 1)
    			{
    
    				fseek (inputFile , 0 , SEEK_SET );	// Position at the next line of text
    
    				src = fgets(buffer, 100, inputFile);	// Read the first line of the file
    
    				printf("\n%s\n", *argv);	// Print the file name
    
    				printf("\nLine: %s\n", src);
    			}
    
    			while(src != NULL && argc > 1)
    			{
    
    				if (*src != '\n')	// Not blank line
    				{
    					rValue = makeargv(src, delmtrs, &argvp);	    // Call makeargv to tokenize the string
    
    					for (i = 0; i < rValue; ++i)	// Print the tokens
    					{
    						printf("\t%s\n", argvp[i]);
    					}
    					printf("\nThe number of tokens in the string is: %d\n\n", rValue);
    				}
    
    				fseek (inputFile , 0 , SEEK_CUR );	// Position at the next line of text
    
    				src = fgets(buffer, 100, inputFile);	// Read the next line
    
    				if (src != NULL)
    				{
    					printf("\nLine: %s\n", src);
    				}
    				else
    					printf("\nEnd of file.\n");
    
    			}
    			fclose(inputFile);	// Close the file
    			argc--;	// Decrement the number of remaining arguments
    			}while (argc > 1);
    	}
    	free(argvp);
    	return 0;

  2. #2
    ATH0 quzah's Avatar
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    This is pretty terrible:
    Code:
    while ((inputFile = fopen (*++argv, "r")) == NULL && argc > 1)
    How about this instead?
    Code:
    for( x = 1; x < argc; x++ )
    {
        inputFile = fopen( argv[ x ], "r" );
        ...
    }

    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    Is the modification to the while loop suspect by increment argv beyond [0]?

    I am not sure what you mean by changing the while loop testing for valid files to a for loop. Is that the implied meaning?

  4. #4
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    Quote Originally Posted by Imanuel View Post
    Is the modification to the while loop suspect by increment argv beyond [0]?
    Yep! because when argv[] is incremented it'll be a null pointer causing fopen() to segfault; so swap the while expressions
    Code:
    while (argc > 1 && (inputFile = fopen (*++argv, "r")) == NULL)
    That's what quzah meant by switching from a while to a for loop - afaict.

  5. #5
    ATH0 quzah's Avatar
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    You will still have a problem, since you aren't ever checking to see if you try to access argv[ NOVALIDINDEX ]. You can't try to access beyond the bounds of an array, which is what he's trying to do.


    Quzah.
    Hope is the first step on the road to disappointment.

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