Getting segmentation fault on function

Question

I have got this function which converts a month from 3 chars to 2 digits month:

int Extract_Month(char *pDestMonth, char *pMonth)
{
    char monthschar[12][4] = { "JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC" };
    char monthsdigit[12][3] = { "01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12" };
    int i = 0;

char tmpStr[4] = "";
tmpStr[0] = (pMonth[0] >= 'a' && pMonth[0] <= 'z') ? ('a' + pMonth[0] - 'A') : pMonth[0];
tmpStr[1] = (pMonth[1] >= 'a' && pMonth[1] <= 'z') ? ('a' + pMonth[1] - 'A') : pMonth[1];
tmpStr[2] = (pMonth[2] >= 'a' && pMonth[2] <= 'z') ? ('a' + pMonth[2] - 'A') : pMonth[2];
tmpStr[3] = 0;

for (i = 0; i < 12; i++)
{
    if (!strncmp(tmpStr, monthschar[i], 3))
    {
        StrMove((uchar *)pDestMonth, (uchar *)monthsdigit[i], 2);
        return 0;
    }
}
return -1;
}

I am running it with gdb and I'm getting a segmentation fault error. Does anyone knows what am i missing here?

I have made some research and I found that seg faults are due to memory mishandling.

gdb output points exactly to this function declaration

This is where the function is being called (reduced code):

provide information on how to call the function with an working example. It might be the case that the input is already wrong. — Martin
– Martin, Commented Jan 22, 2019 at 13:48
(pMonth[0] >= 'a' && pMonth[0] <= 'z')? Don't you mean islower()? Or you can just use toupper(). — Andrew Henle
– Andrew Henle, Commented Jan 22, 2019 at 13:51
gdb will tell you which line is crashing if you compile with '-o0 -g'. Note also that your upper-case conversion is wrong - work it through for 'a', for example. — EML
– EML, Commented Jan 22, 2019 at 14:06

darune · Accepted Answer · 2019-01-22 14:31:38Z

5

You are making something really simple in an extremely complicated way..

Since you flagged it c++, you can just use a map and return by lookup like this:

std::string Extract_Month_As_Digits(const std::string& month)
{
  static std::map<std::string, std::string> monthToDigit = {{"JAN", "01"}};//omitted init.
  auto found = monthToDigit.find(month);
  return found  != monthToDigit.end() ? *found : "";
}

If you want an exception thrown on bad input/lookup, you may reduce it to return monthToDigit.at(month);

edited Jan 22, 2019 at 14:31

answered Jan 22, 2019 at 14:22

darune

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2 Comments

xtofl Over a year ago

Nice one! If you choose to use monthToDigit.at(...), you get error handling for free, too.

user7860670 Over a year ago

At least OP is (trying to) doing it without multilevel dynamic memory allocation, exceptions, stl and relying on dynamic initialization and finalization. This solution would be definitely a better match to be called "making something really simple in an extremely complicated way"

xtofl · Accepted Answer · 2019-01-22 14:22:43Z

1

You're making it very complex. Simplifying the solution may result in a function that does no strcpy whatsoever:

int month_index(const char *threeDigitMonth) {
    static const char *names[] = {"JAN", "FEB", NULL};
    const char** name = names;
    while(name && strcmp(threeDigitMonth, *name)){ ++name; }
    return name - names;
}

Now your problem is reduced to converting an int into a two-digit string, something snprintf is very capable of.

Or you could use C++:

auto month_index(const std::string& threeDigitMonth) {
  static const std::unordered_map<
     std::string, std::string> months = {{
       {"JAN", "01"},
       {"FEB", "02"},
       ...
    }};
    return months.at(threeDigitMonth);
  }

edited Jan 22, 2019 at 14:22

answered Jan 22, 2019 at 14:12

xtofl

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