Edit: Sorry, it should be c++. how to use strtok in string?
FQ_ID_line[0]="1,26665;TUK.006.8955.FQ;TUK;400 BB 2 FQ;400 BB 2;899;FQ;Z_SCCFG1;Z_BSCFG1;333";
FQ_ID_line[1]="2,26223;TUK.002.8955.FQ;TUK;400 BB 2 FQ;400 BB 2;;FQ;Z_SCCFG1;Z_BSCFG1;333";
for(int FQ_i=0;FQ_i<FQ_Number;FQ_i++)
{
printf( "FQ_ID_line[FQ_i]=%u\n", FQ_ID_line[FQ_i] );
char * FQ_array=strdup(FQ_ID_line[FQ_i].c_str());
char *chars_array=strtok(FQ_array,seps);
chars_array=strtok(NULL,seps);
strcpy(DataLine[FQ_i].analog_comp_id,chars_array);
chars_array=strtok(NULL,seps);
strcpy(DataLine[FQ_i].RTU_abbr,chars_array);
chars_array=strtok(NULL,seps);
chars_array=strtok(NULL,seps);
chars_array=strtok(NULL,seps);
chars_array=strtok(NULL,seps);
chars_array=strtok(NULL,seps);
strcpy(DataLine[FQ_i].analog_scc_fep_group,chars_array);
chars_array=strtok(NULL,seps);
strcpy(DataLine[FQ_i].analog_bsc_fep_group,chars_array);
chars_array=strtok(NULL,seps);
strcpy(DataLine[FQ_i].RTU_number,chars_array);
DataLine[FQ_i].float_RTU_number=atof(chars_array);
free(FQ_array);
}
the ouput is :
DataLine[0].analog_comp_id=TUK.006.8955.FQ
DataLine[0].RTU_abbr=TUK
DataLine[0].analog_scc_fep_group=Z_SCCFG1
DataLine[0].analog_bsc_fep_group=Z_BSCFG1
DataLine[0].float_RTU_number=333
DataLine[1].analog_comp_id=TUK.002.8955.FQ
DataLine[1].RTU_abbr=TUK
DataLine[1].analog_scc_fep_group=Z_BSCFG1
DataLine[1].analog_bsc_fep_group=333
DataLine[1].float_RTU_number=
I want to the ouput:
DataLine[0].analog_comp_id=TUK.006.8955.FQ
DataLine[0].RTU_abbr=TUK
DataLine[0].analog_scc_fep_group=Z_SCCFG1
DataLine[0].analog_bsc_fep_group=Z_BSCFG1
DataLine[0].float_RTU_number=333
DataLine[1].analog_comp_id=TUK.002.8955.FQ
DataLine[1].RTU_abbr=TUK
DataLine[1].analog_scc_fep_group=Z_SCCFG1
DataLine[1].analog_bsc_fep_group=Z_BSCFG1
DataLine[1].float_RTU_number=333
The cause of the problem:
The function strtok() has many problems, due to the fact that subsequent calls depend on previous calls, and this dependency is managed in an unsafe manner:
it's not thread safe (see Robert's comment, and C++ standard section 21.8 pt 14)
if one function you call would use strtok() without you knowing, your next call to strtok() would return a lot of surprises.
Now your problem comes from the input string part: ...400 BB 2;;FQ;..., and the definition of strtok() : In subsequent calls, the function (...) uses the position right after the end of last token as the new starting location for scanning. To determine the beginning and the end of a token, the function first scans from the starting location for the first character not contained in delimiters (which becomes the beginning of the token)
So everything works well until it returns "400 BB 2". The next ";" will according to this algorithm be skipped and your code will jump over the empty field (;;) as if it didn't exist. Not ony do you have a shift in the following fields, but your last call to strtok() may even cause segmentation fault.
Solution:
Best avoid strtok(). If you like c-style, you may consider instead the use of strpbrk() with some adaptation in your code. For example:
char* get_field(char*p, char*& next, const char* s) // by ref as it's c++
{
if ((next = strpbrk(p, s)) != NULL)
*next++ = '\0';
return p;
}
with the following usage to replace strtok():
char* next;
char *chars_array = get_field(FQ_array, next, seps);
...
chars_array = get_field(next, next, seps); // instead of strtok(NULL, seps)
...
My personal recommendation, with C++, would be to consider regex expressions provided in the standard (or in boost), which would also allow for consistency check on you input data.
The full code would then look like:
regex fmt("([0-9]*,[0-9]*);(.*);(.*);(.*);(.*);(.*);(.*);(.*);(.*);([0-9]*\.*[0-9]*)");
for (int FQ_i = 0; ...)
{
smatch sm;
printf("FQ_ID_line[FQ_i]=%u\n", FQ_ID_line[FQ_i]); // ok, a cout would be better
if (regex_match(FQ_ID_line[FQ_i], sm, fmt)) {
DataLine[FQ_i].analog_comp_id = sm[2];
DataLine[FQ_i].RTU_abbr = sm[3];
DataLine[FQ_i].analog_scc_fep_group = sm[8];
DataLine[FQ_i].analog_bsc_fep_group = sm[9];
DataLine[FQ_i].RTU_number = sm[10];
DataLine[FQ_i].float_RTU_number = stof(sm[10]);
}
else
cout << " ** Non matching line ignored !!\n";
}
By fine tuning the regex, you could then check even more for consistency before assigning (Here I just did the minimum for the sake of the example).
Related
Can someone briefly explain how to get a character from index from String in C++.
I need to read the first 3 letters of a String and in java it would bestr.charAt(index) and I have been searching the internet for a solution for 2h now and still don't understand...
can some one please give me an example.
std::string provides operator[] to access a character by index:
https://en.cppreference.com/w/cpp/string/basic_string/operator_at
Example:
const std::string s("hello");
const char c = s[0];
// c is set to ‘h’
substr()
It returns a newly constructed string object with its value initialized to a copy of a substring of this object.
Syntax
substr(pos, pos+len)
Code
std::string str ("Test string"); //string declaration
string sub_string = str.substr(0,3);
String index starts from 0.
Best place to look would be cpluspluc.com: http://www.cplusplus.com/reference/string/string/
You may use as earlier mentioned: http://www.cplusplus.com/reference/string/string/operator[]/
std::string str ("Test string");
for (int i=0; i<str.length(); ++i)
{
std::cout << str[i];
}
Or better yet: http://www.cplusplus.com/reference/string/string/at/
std::cout << str.at(i);
which also checks for a valid position and throws an out of range exception otherwise.
Alternatively you could use http://www.cplusplus.com/reference/string/string/data/
to acces the raw data.
Or if you want to check that your string starts with a specific pattern: http://www.cplusplus.com/reference/string/string/rfind/
std::string str = "Hey Jude!";
if (str.rfind("Hey", 0) == 0) {
// match
}
Another option to obtain a single character is to use the std::string::at() member function. To obtain a substring of a certain length, use the std::string::substr member function.
The problem asks to create a program that asks the user to enter some text and that text will be surrounded by asterisks depending on the width of the screen for example if the user inputs "Hello world" the output should be:
****************
* Hello World! *
****************
I've tried to create the functions but I'm stuck becaus of a compiler error with the shown minimal code.
Question: Why does it tell me no matching function for within_width(text, 80)?
Some of the code I have is below:
#include <iostream>
#include <string>
void display_header (std::string &header) {
std::string text;
header = text;
}
bool within_width (std::string& text, unsigned short int& max_width) {
}
int main() {
std::string text;
std::cout << "Please enter header text: ";
std::getline(std::cin, text);
if (within_width(text, 80)) {
// call the display_header function and pass in the text
// inputted by the user
} else {
std::cout << text;
}
return 0;
}
This declaration of the function
bool within_width (std::string& text, unsigned short int& max_width)
asks for an unsigned short int variable, because it has a reference parameter, see the second &.
To satisfy it, you need to put the value 80 into a variable and give the variable as parameter.
unsigned short int MyWidth=80;
if (within_width(text, MyWidth))
Alternatively (but I assume you are not allowed) you can use a call by value parameter
bool within_width (std::string& text, unsigned short int max_width)
Then you could call as shown.
I won't give a full answer to the exercise here, just some clues.
the display_header() and within_width() functions need to know the string given in parameters but may not modify it ; thus the type of this parameter should be const std::string & (the const was missing).
the second parameter of the within_width() function is just an integer that will be compared to the length of the string ; you don't need to pass it by reference (or at least const), rather by value. Here, the (non-const) reference prevents from passing the literal constant 80.
(it seems to be the main concern of the question after edition)
You need to reason step by step.
all of this depends on the size of the string (12 for Hello World!) ; this information is available via size(text) (or text.size())
(https://en.cppreference.com/w/cpp/iterator/size)
(https://en.cppreference.com/w/cpp/string/basic_string/size)
This size will have to be compared to max_width
Displaying the line with header will require 4 more characters because * will be prepended and * will be appended.
Thus the two surrounding lines will have the length size(header)+4 too.
In order to create such a string made of *, you could use a constructor of std::string taking two parameters : the count of characters and the character to be repeated.
(https://en.cppreference.com/w/cpp/string/basic_string/basic_string)
Send all of this to std::cout in the correct order.
Edit: Just noticing that this answer probably goes far beyond the scope of the task you have been given (just filling in some skeleton that has been provided by your teacher).
I'll still leave it here to illustrate what could be done with arbitrary input. Maybe you want to experiment a little further than what you have been asked...
bool within_width(...)
Pretty simple: string.length() <= max – just wait a second, you need to consider asterisks and spaces at beginning and end of output, so: max - 4
But you can do better, you can split the string, best at word boundaries. That's a bit difficult more difficult, though:
std::vector<std::string> lines;
// we'll be starting with an initially empty line:
auto lineBegin = text.begin();
auto lineEnd = text.begin();
for(auto i = text.begin(); i != text.end(); ++)
// stop condition empty: we'll stop from inside the loop...
{
// ok, we need to find next whitespace...
// we might try using text.find_first_of("..."), but then we
// need to know any whitespace characters ourselves, so I personally
// would rather iterate manually and use isspace function to determine;
// advantage: we can do other checks at the same time, too
auto distance = std::distance(lineBegin, i);
if(std::distance(lineBegin, i) > maxLineLength)
{
if(lineEnd == lineBegin)
{
// OK, now we have a problem: the word itself is too long
// decide yourself, do you want to cut the word somewhere in the
// middle (you even might implement syllable division...)
// or just refuse to print (i. e. throw an exception you catch
// elsewhere) - decide yourself...
}
else
{
lines.emplace_back(lineBegin, lineEnd);
lineBegin = lineEnd; // start next line...
}
}
// OK, now handle current character appropriately
// note: no else: we need to handle the character in ANY case,
// if we terminated the previous line or not
if(std::isspace(static_cast<unsigned char>(*i)))
{
lineEnd = i;
}
// otherwise, we're inside a word and just go on
}
// last line hasn't been added!
lines.emplace_back(lineBegin, lineEnd);
Now you can calculate maximum length over all the strings contained. Best: Do this right when adding a new line to the vector, then you don't need a separate loop...
You might have noticed that I didn't remove whitespace at the end of the strings, so you wouldn't need to add you own one, apart, possibly, from the very last string (so you might add a lines.back() += ' ';).
The ugly part, so far, is that I left multiple subsequent whitespace. Best is removing before splitting into lines, but be aware that you need to leave at least one. So:
auto end = text.begin();
bool isInWord = false; // will remove leading whitespace, if there is
for(auto c : text)
{
if(std::isspace(static_cast<unsigned char>(c)))
{
if(isInWord)
{
*end++ = ' '; // add a single space
isInWord = false;
}
}
else
{
*end++ = c;
isInWord = true;
}
}
This would have moved all words towards the beginning of the string, but we yet to drop the surplus part of the string yet contained:
text.erase(end, text.end());
Fine, the rest is pretty simple:
iterate over maximum length, printing a single asterisk in every loop
iterate over all of your strings in the vector: std::cout << "* " << line << "*\n";
repeat the initial loop to print second line of asterisks
Finally: You introduced a fix line limit of 80 characters. If console is larger, you just won't be using the entire available width, which yet might be acceptable, if it is smaller, you will get lines broken at the wrong places.
You now could (but that's optional) try to detect the width of the console – which has been asked before, so I won't go any deeper into.
Final note: The code presented above is untested, so no guarantee to be bugfree!
I'm new at MFC and I need to do something which sounds extremely simple: determining if a string only contains hexadecimal characters.
For that, I browse through the string (it's a CString) and I verify all characters using the FindOneOf() method, as follows:
int iTest = CString(pszText[i]).FindOneOf((LPCWSTR)"0123456789ABCDEFabcdef");
For some bizarre reason, I always get -1 as a result.
What am I doing wrong?
P.s.1 I prefer not to use the SpanIncluding() method, I find the FindOneOf() quite readable but I don't know how to use it.
P.s.2 Also simple STL seems not to be working: I tried to work with std::isxdigit(pszText[i]) but in order to get this to work, I need to include <locale> and then this function is asking for a second parameter, next to the character I want to check, and a null-pointer is not allowed there (std::isxdigit(pszText[i], nullptr) does not work).
There are several problems in your code:
This is wrong:
int iTest = CString(pszText[i]).FindOneOf(LPCWSTR)"0123456789ABCDEFabcdef");
It should be:
int iTest = CString(pszText[i]).FindOneOf(L"0123456789ABCDEFabcdef");
The cast will simply make the compiler believe that "0123..." is a wide string but it isn't. You need to use the L prefix to indicate that the string is a wide string.
But even then your algorithm won't work because FindOneOf will simply find the first occurrence of any of the characters in the parameter.
Example:
int iTest = CString(L"Z223Zbc").FindOneOf(L"0123456789ABCDEFabcdef");
"Z223Zbc" is obviously not a hexadecimal string, but iTest will contain 1 because the first character of "Z223Zbc" being part of "0123456789ABCDEFabcdef" is '2' and that's at position 1.
iTest will only contain -1 if the string to be tested doesn't contain any hexadecimal characters as for example "xyz".
Therefore this solution is appropriate:
#include <cwctype>
...
WCHAR string[] = L"123abcX";
bool ishexstring = true; // assume the string is a hex string
for (int i = 0; ; i++)
{
WCHAR c = string[i];
if (c == 0)
break; // end of string => we exit the looop
if (!std::iswxdigit(c))
{
ishexstring = false; // c is no hex digit
break; // exit loop
}
}
This algorithm should be put into a function, but I'm leaving this as an exercise for the reader.
Solution using SpanIncluding (less efficient because we need tot construct a temporary CString):
bool ishexstring = CString(string).SpanIncluding(L"0123456789ABCDEFabcdef") == str;
working on a c++ project, I need to iterate on a string ( or char* depending the solution you could provide me ! ). So basically I'm doing this :
void Pile::evalExpress(char* expchar){
string express = expchar
regex number {"[+-*/]"};
for(string::iterator it = express.begin(); it!=express.end(); ++it){
if(regex_match(*it,number)){
cout<<*it<<endl;
}
}
}
char expchar[]="234*+";
Pile calcTest;
calcTest.evalExpress(expchar);
the iterator works well ( I can put a cout<<*it<<'endl above the if statement and I get a correct output )
and then when I try to compile :
error: no matching function for call to 'regex_match(char&, std::__cxx11::regex&)'
if(regex_match(*it,number)){
^
I have no idea why this is happening, I tried to don't use iterator and iterate directly on the expchar[i] but I have the same error with regex_match()...
Regards
Vincent
Read the error message! It tells you that you're trying to pass a single char to regex_match, which is not possible because it requires a string (or other sequence of characters) not a single character.
You could do if (std::regex_match(it, it+1, number)) instead. That says to search the sequence of characters from it to it+1 (i.e. a sequence of length one).
You can also avoid creating a string and iterate over the char* directly
void Pile::evalExpress(const char* expchar) {
std::regex number {"[+-*/]"};
for (const char* p = expchar; *p != '\0'; ++p) {
if (regex_match(p, p+1, number)) {
cout<<*p<<endl;
}
}
}
How can i replace multiple occurrences of a character with a string containing the occurrence number.
e.g if i have the following expression.
insert into emp values(?,?,?)
I want the following converted string.
insert into emp values(_p_1,_p_2,_p_3)
I am trying this using the boost regular expression.
Can anyone tell me how to achieve this using the boost c++ (with no or minimum iteration).
currently I am using the following approach:
std::wstring q=L"insert into emp values(?,?,?)";
auto loc = q.find(L"?");
auto len = wcslen(L"?");
auto c=1;
while(loc != std::wstring::npos)
{
q.replace(loc, len , L"_p_"+to_wstring(c));
c++;
loc = q.find(L"?");
}
cout<<q.c_str();
Please suggest better and efficient approaches.
I'd just forget regular expressions and trying to do this simple thing with Boost.
It's like asking, "how do I add 1 to a variable using Boost regular expressions"?
Best answer, IMHO, is to instead just use ++ for the task of adding 1, and to use a loop to replace special characters with strings.
string const query_format = "insert into emp values(?,?,?)";
string const params[] = {"_p_1", "_p_2", "_p3"};
string query;
string const* p = params;
for( char const c : query_format )
{
if( c == '?' ) { query += *p++; } else { query += c; }
}
// Use `query`
One might choose to wrap this up as a replace function.
Disclaimer: code not touched by compiler.
If you control the query_format string, why not instead make the placeholders compatible with Boost format.
Re the parenthetical requirement
” with no or minimum iteration
there's iteration involved no matter how you do this. You can hide the iteration behind a function name, but that's all. It's logically impossible to actually avoid the iteration, and it's trivial (completely trivial) to hide it behind a function name.