Thread: program crashing despite no errors and warnings

there are three ways using argc, argv

Code:

int main(int argc, char **argv);

Code:

int main(int argc, char *argv[]);

Code:

int main(int argc, char argv[][]);

Try this:

Code:

int main (int argc, char *argv[])

Originally Posted by yohanevindra

ohh..and in the print statement where i print out the strings which need to be compared to and the input argument, when i run this program, it jus gives out weird symbols..not what has been input..

Code:

printf("\n %s %s %s %s",&inputVar,&initInput,&turnInput,&simInput);

Lose the & in front of each string variable in your printf statement. Also, main returns an int - so don't make the return type void. Furthermore, because main returns an int, you should put a return statement at the end of the main function (unless you are trying to conform to C99, where you don't necessarily need to put an explicit return statement there).

Code:

void main (int argc, char** argv[])

Your argument vector is not declared properly. As others have indicated, you should do it something like this:

Code:

int main(int argc, char *argv[])

Edit: What sort of warnings have you got turned on for your compiler? It should have complained about some of the things you are doing with your code.

[edit] kermit has beaten me to the post. Sorry about duplication. [/edit]

Why not to use void main(): SourceForge.net: Void main - cpwiki

Standard practice is to print newlines after a line of text, not before. This can be important when you're using print statements for debugging purposes, since the console may not flush (display some text) until a newline is printed, making you think the debugging message wasn't reached when in fact it was.

If a variable is declared as char *inputvar; then it is a pointer to an array of characters, that is, a string. So if it was pointing to a valid string, you could use something like

Code:

printf("%s\n", inputvar);

But as soon as you go &inputvar, you get a pointer to a string, which will crash printf() quite handily.

Also, argv[0] is the name of the program, not the first parameter passed. Use argv[1], after making sure it exists by ensuing that argc >= 2.

Last note: as you may be aware, using char* pointers as strings is fine as long as the data you're pointing to exists. For example, you can say

Code:

char *flag = "-t";

because "-t" is a string literal and is stored in static memory. You can also assign a char* pointer to some data from argv[], because the program which executed your program made space for and is storing the argv[] array. But you cannot read data from the user into a char* pointer unless you make the pointer point at a memory region you can fill in. You could use e.g.

Code:

char *data = malloc(10);
fgets(data, 10, stdin);
free(data);

or

Code:

char data[10];
fgets(data, sizeof data, stdin);

if you wanted to get user input, for example.

For online tutorials about pointers, have a look at this and this.

The material for the second link is done by someone who used to be a regular here on this board. In my opinion, she is a first rate programmer who really knows her stuff. You won't go wrong on either link though, so give them both a good going over.

For the compiler (which is gcc, by the way, and is an excellent compiler), you will want to turn on -Wall and -Wextra. The -Wall switch is a little bit deceiving, as it does not really turn on "all" warnings (though it turns on quite a few. You can read about which ones in the man page linked below). The -Wextra switch turns on quite a few more warning switches that -Wall doesn't get (again, see the manual page for details). Between these two, you will be covering an awful lot of the important things, especially for someone just starting out. Pay attention to the warnings they produce, and you will find yourself learning a bit too. You may as well give the gcc man page a read. It is a lot to look at, and you certainly don't need to know it all, but give it a skim, to gain a general idea of what is available to you, and then slowly read it bit by bit to know it better over time.

Right, I'm pretty sure you understand this, but pay attention to those warnings, Don't go disabling them or ignoring them. Fix them.
If you don't understand them, ask. Ignoring them is a sure way to mess up your program, and fixing them goes a long way towards fixing a lot of bugs.
Oh and Code::Blocks is an IDE, not a compiler. GCC is usually the compiler used by it, though it can use more.