strcmp issue

idk why but i cannot figure out what is wrong with my program. i found it crashes on strcmp but as far as i can tell this is how i have always used it. i'll post what i think are the impotent parts.

Code:

        FILE* fin;							//file pointer
	fin = fopen("profiles.data", "r");	//open file

	if(fin == NULL)
	{
		printf("ERROR opening file\n");
		return -1;
	}

	char* input = "";					//input form file.
	fscanf(fin, "%[^\n]", &input);		//read line

	//initialize data liked list
	initializeData(); //<----dont think this matters it never touches input or anything else

	printf("%s ?= **\n", &input); //<----this works

	//look for start of file. start of file will contain "**" on a single line by it self.
	while(strcmp(input, "**") != 0) //<---crashes here
	{
		fscanf(fin, "%[^\n]", &input);
	}

//more to do after this...

EDIT fixed =! to !=. this was right in my code just wrong here.

=! should probably be !=, but I would expect you to get a compile error rather than a runtime crash.

By the way, is this supposed to be C or C++?

EDIT: Clarity.

Beginner here so actual question:

So what happens when you enter the while loop and there are no more "**" in the file and you reach the EOF?

Where do you allocate space for the variable input? (I mean what it points to)
I see you declare it as a pointer to char; I just see no place you allocate enough space to hold 3 bytes of data pointed to by it.

Tim S.

laserlight

=! should probably be !=, but I would expect you to get a compile error rather than a runtime crash.

By the way, is this supposed to be C or C++?

in my code is it "!=" idk why it is wrong here. and this is C++ code.

Beginner here so actual question:

So what happens when you enter the while loop and there are no more "**" in the file and you reach the EOF?

the file is set up so that the ** indicates the start of the data in the file. if there is no ** then the data file is set up wrong and seeing as i set up the data file it would fix that.

stahta01

Where do you allocate space for the variable input? (I mean what it points to)
I see you declare it as a pointer to char; I just see no place you allocate enough space to hold 3 bytes of data pointed to by it.

Tim S.

i do not recall needing to allocate space for scanf or fscanf. how ever i did find it strange that i had a compiler error when i tried to read in the strings with out the '&'. i was under the impression that strings were already pointers and the variable didn't need the '&'. and the printf works fine with the '&'

this is also my first time really programming in C++ so basic differences may not be know to me.

EDIT: more info

Originally Posted by t014y

this is C++ code.

Is there any specific reason that you are using C-style I/O over C++-style I/O? Note that you can work with std::string objects instead of dealing with null terminated strings.

Is there any specific reason that you are using C-style I/O over C++-style I/O? Note that you can work with std::string objects instead of dealing with null terminated strings.

the reason is simply because I'm used to C-stile I/O. i didn't think it would make a difference.

Originally Posted by t014y

i do not recall needing to allocate space for scanf or fscanf. how ever i did find it strange that i had a compiler error when i tried to read in the strings with out the '&'. i was under the impression that strings were already pointers and the variable didn't need the '&'. and the printf works fine with the '&'EDIT: more info

You do need to allocate the memory. You pass a pointer to pointer, instead of pointer to buffer, which results (probably, there might be another bug) in crash. Additionaly, you cast away the const-correctness when assigning a string literal to a char* variable. (the literal has type const char*)

Code:

char input[256];
fscanf(fin, "%s", input);		// I changed it to %s; I dont even know what this C-style rubbish meant

i changed it to be more C++ like and it seems to work now. still dont know why it didn't work before. the %[^\n] reads in a whole line where %s reads in a string that is the reason i was using that.

now that section of code looks like this...

Code:

	ifstream fin;							//file pointer
	fin.open("profiles.data");				//open file

	if(!fin.is_open())
	{
		printf("ERROR opening file\n");
		return -1;
	}

	string input = "";						//input form file.

	getline(fin, input);

	//initialize data liked list
	initializeData();

	//look for start of file. start of file will contain "**" on a single line by it self.
	while(input.compare("**") != 0)
	{
		cout << input << "\n";
		//fscanf(fin, "%[^\n]", &input);
		getline(fin, input);
	}

thanx for the help. if you see any issues that might come up from this plz let me know.