Thread: Problem with strings and filenames

Hi,

I have made this a simple command-line program which reads through a file and changes a few characters (ie, all "9" are replaces with "8"). It takes only a single argument, which is the input file. Now I want to make the output to be preceeded by a "_".

This is the code I came up with after reading about some string functions:

Code:

char * filename = malloc( strlen(argv[1]) + 1);
strcpy(filename, "_");
strcat(filename, argv[1]);

FILE *fp = fopen(filename, "wb");    /* Creates new file */

It works when calling "my_app my_file.txt" from the console, however when I drag and drop a file from Windows, the argument includes the full path, so I get something like argv[1] = "C:\my_file.txt". When the "_" character is appended, the filename string is "_C:\my_file.txt", which crashes fopen, instead of "C:\_my_file.txt".

Can someone give a practical example how to deal with this? I'm not sure how to deal with this string modification.

Use one of the string finder things to look for the last \ in your filename (hint: it's strrchr). That's where you want to put the _.

Code:

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

char *AppendNewFilename(const char *oldFilename, char pattern)
{
	if(!oldFilename)
	{
		fprintf(stderr, "Invalid parameter for filename:{NULL}.\n");
		return NULL;
	}
	else
	{
		unsigned int nFileLen = strlen(oldFilename)+2;
		/* Allocate 2 more bytes one for '\0' and one for the pattern. */
		char *generatedFilename = calloc(nFileLen, sizeof(char));
		if(!generatedFilename)
		{
			fprintf(stderr, "Memory Allocation Error.\n");
			return NULL;
		}
		else
		{
			unsigned int index, jndex;
			for(index = 0, jndex = 0; index < nFileLen-1; index++)
			{
				if(index == 3)
				{
					generatedFilename[index] = pattern;
					continue;
				}
				generatedFilename[index] = oldFilename[jndex++];
			}
			if(index == nFileLen-1)
			{
				generatedFilename[index] = '\0';
				return generatedFilename;
			}
			else
			{
				fprintf(stderr,"For Loop Error.\n");
				return NULL;
			}
		}
	}
}

int main(int argc, char *argv[])
{
	char *testfile = AppendNewFilename("C:\\my_file.txt", '_');
	puts(testfile);
	free(testfile);
	printf("Hit enter to continue...\n");
	getchar();
}