Input validation and Error handling in C?

[nateuni]

Hi,

I am new to programming.. and am studying IT at Uni

Over the weekend, I managed to write a java class that handles errors and loops until receiving valid input for a range of different datatypes. I am looking to write something like this in C (as my other subject deals with C). I have been googling etc and still have not really come up with what I want. Now I am aware that C++ has the try/catch option like Java, but what do I have available in C? The books I looked at didnt address my issue, and I have skipped around trying to find an answer, so i thought i might try here.

What do I do to make sure that my scanf ("*i", &myInt) statements get their correct input and not some char that makes it fall through the questionnaire in my code ..and so,..?

Help??

Thanks.. in advance.
Nate

[kvprajapati]

Read this article at Dr.Dobb's http://www.ddj.com/cpp/184402023

SUMMARY: Standard Library string functions like strcpy() are not considered secure by today's standards. The Managed String Library is one possible solution.

And here is a link of a very good book Secure Programming Cookbook for C and C++

[Tom Gunn]

Now I am aware that C++ has the try/catch option like Java, but what do I have available in C?

C can simulate exception handling with the setjmp.h library, but that is kind of an advanced C thing. ;) Usually error handling in C is done by receiving error codes as the return value from functions, as output parameters to functions, or with a global error code object:

#include <stdio.h>

#if defined(_MSC_VER)
#define FLUSH(strm) ((strm)->_cnt = 0)
#else
#define FLUSH(strm) FlushInputStream(strm)
#endif

void FlushInputStream(FILE *strm)
{
    int ch;
    do ch = getc(strm); while (ch != '\n' && ch != EOF);
}

void PrintError(char const* msg, FILE *istrm)
{
    fputs(msg, stderr);
    FLUSH(istrm);
}

/* error handling with a return code */
int GetInt1(int* value)
{
    return scanf("%d", value) == 1 &&
           0 < *value && *value < 6;
}

/* error handling with an output parameter */
int GetInt2(int* error)
{
    int value = 0;

    if (!(scanf("%d", &value) == 1 &&
          0 < value && value < 6))
    {
        *error = 1;
    }

    return value;
}

static int errorCode;

/* error handling with a global error object */
int GetInt3()
{
    int value = 0;

    errorCode = !(scanf("%d", &value) == 1 &&
                  0 < value && value < 6);

    return value;
}

int main()
{
    int value;
    int error;

    /* error handling with a return code */
    if (GetInt1(&value)) printf("read %d\n", value);
    else PrintError("GetInt1 failed\n", stdin);

    /* error handling with an output parameter */
    error = 0;
    value = GetInt2(&error);
    if (error == 0) printf("read %d\n", value);
    else PrintError("GetInt2 failed\n", stdin);

    /* error handling with a global error object */
    errorCode = 0;
    value = GetInt3();
    if (errorCode == 0) printf("read %d\n", value);
    else PrintError("GetInt3 failed\n", stdin);
}

Do you already have your code set up to recognize different error cases? Stream input in C is tricky. ;)