7: Storing Sequences in Arrays in .NET

Encoder PDF 417 in .NET 7: Storing Sequences in Arrays

// safer alternative // cingetline(szString1, 128); // now the second string char szString2[128]; cout << Enter string #2: ; cin >> szString2; // safer alternative // cingetline(szString1, 128); // accumulate both strings into a single buffer char szString[260]; // copy the first string into the buffer strncpy(szString, szString1, 128); // concatenate a - onto the first strncat(szString, - , 4); // now add the second string strncat(szString, szString2, 128); // and display the result cout << \n << szString << endl; // wait until user is ready before terminating program // to allow the user to see the program results system( PAUSE ); return 0; }

The Concatenate program reads two character strings and appends them together with a - in the middle The arguments to the str() functions appear backward to any reason able individual (you might consider this an acid test for reasonable ) For example, the function strncat(target, source, count) tacks the second string source onto the end of the first argument target An example output from the program appears as follows:

The program begins by reading a string from the keyboard cin >> szString1 stops when any type of whitespace is encountered Characters up to the first whitespace are read, the whitespace character is tossed, and

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the remaining characters are left in the input hopper for the next cin>> statement Thus, if I were to enter the Dog , szString2 would be filled with the , and the word Dog would be left in the input buffer The cin >> extractor knows nothing about the length of the string cin is perfectly willing to read thousands of characters and stuff them into szString1, even though it is declared 256 characters long This causes a dangerous overflow condition that hackers can (and will) exploit to put a virus in your program C++ provides work-arounds for many of the string overflow problems For example, the function getline() inputs a line of text; however, this function accepts the length of the string as one of its arguments:

cingetline(string, lengthOfTheString);

(Ignore the strange looking cin format for now) The strncpy() and strncat() functions accept the length of the target buffer as one of their arguments The call strncpy(szString, szString1, 128) says copy the characters in szString1 into szString until you copy a null character or until you ve copied 128 characters, whichever comes first The call specifically does not mean copy 128 characters every time There are both counting and noncounting versions of most of the str() functions The noncounting versions don t require the maximum number of characters to process as an argument You can use these when you don t know the buffer size, but be aware that they are perfectly happy to write beyond the end of the target string

ANSI C++ includes a type string designed to make it easier to manipulate strings of text I use the term string to refer to an array of characters terminated by a null and string type to refer to the type string The string type includes opera tions for copying, concatenating, capitalizing, knotting, and simple magic tricks string avoids the overrun problems inherent with null terminated strings The functions that manipulate string objects are defined in the include file <string> The string type based StringConcatenate program appears as follows:

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// StringConcatenate - concatenate two string type // variables with a - in the middle #include <cstdio> #include <cstdlib> #include <iostream> #include <string> using namespace std; int main(int nNumberofArgs, char* pszArgs[]) { // read first string string string1; cout << Enter string #1: ; cin >> string1; // now the second string string string2; cout << Enter string #2: ; cin >> string2; // accumulate both strings into a single buffer string buffer; string divider = - ; buffer = string1 + divider + string2; // and display the result cout << \n << buffer << endl; // wait until user is ready before terminating program // to allow the user to see the program results system( PAUSE ); return 0; }

This concatenate function defines two variables, string1 and string2 (clever, no ) A string type variable is not defined of any specified length it can grow and shrink to fit the number of characters it contains (up to avail able memory, of course, or the cows come home, whichever is first) Not only do you not have to guess how big to make a target character array, but some nefarious user can t crash your program by inputting too many characters The StringConcatenate program manipulates the string type variables as it would any other Notice that some operations have to be understood in a slightly different way from their arithmetic equivalent For example, to add two string type vari ables together means to concatenate them In addition, notice how C++ can convert a null terminated character string into a string type variable with out being told to

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