I want to write myself a function similar to PHP's str_repeat. I want this function to add specified amount of characters at the end of string.
This is a code that does not work (string argument 2 expected!)
void chrrepeat(const char &ch, string &target, const int &count) {
for(int i=0; i<count; i++)
strcat(target, ch);
}
I don't exactly know what language is that (C++?), but you seem to be passing a char to strcat() instead of a null-terminated string. It's a subtle difference, but strcat will happily access further invalid memory positions until a null byte is found.
Instead of using strcat, which is inefficient because it must always search up to the end of the string, you can make a custom function just for this.
Here's my implementation in C:
void chrrepeat(const char ch, char *target, int repeat) {
if (repeat == 0) {
*target = '\0';
return;
}
for (; *target; target++);
while (repeat--)
*target++ = ch;
*target = '\0';
}
I made it return an empty string for the case that repeat == 0 because that's how it works in PHP, according to the online manual.
This code assumes that the target string holds enough space for the repetition to take place. The function's signature should be pretty self explanatory, but here's some sample code that uses it:
int main(void) {
char test[32] = "Hello, world";
chrrepeat('!', test, 7);
printf("%s\n", test);
return 0;
}
This prints:
Hello, world!!!!!!!
Convert char to string.
void chrrepeat(char ch, string &target, const int count) {
string help = "x"; // x will be replaced
help[0] = ch;
for(int i=0; i<count; i++)
strcat(target, help);
}
Related
I try to read the name of a file using scanf but failed.
I am very bad at pointers and could not find the problem.
Is there a problem with the pointer to the array of string?
Here is my code:
int* Read_file(char* str[])
{
FILE* fp = fopen(str[1], "r");
if(fp == NULL)
{
printf("File cannot open\n");
return NULL;
}
int rows = 0;
while(!feof(fp))
{
if(fgetc(fp) == '\n')
{
rows ++;
}
}
rows ++;
int* keys = (int*)malloc(3 * rows * sizeof(int));
fseek(fp, 0L, 0);
while(!feof(fp))
{
for(int i = 0;i < rows;i ++)
{
for(int j = 0;j < 3;j ++)
{
fscanf(fp,"%d", &keys[(3 * i) + j]);
}
}
}
fclose(fp);
return keys;
}
int main()
{
char* str[20];
printf("Build_tree ");
scanf("%s",&str);
int* keys = Read_file(str);
return 0;
}
Okay, so the thing is:
You need a char array to store a string(file-name). So you should use a char array. Instead, you were using an array of char pointers.
An array is actually a series of memory blocks. The name of the array represents a pointer to the first element of the array(in this case the first char variable).
While reading a string, scanf needs a location to store it. So you need to give it the address of the first char variable of your char array, which is available in your char array itself. So you have to pass str only to scanf. In the case of normal int,float, and such fundamental data types, their names represent memory blocks and not pointers to memory blocks, and hence you had to use a &.
Then for fopen, fopen expects a char*(which points to the first character of the char array stoing the filename) and you have to provide it with a char* . So you should pass str.
I think your code should go like
int* Read_file(char str[])
{
FILE* fp = fopen(str, "r");
if(fp == NULL)
{
printf("File cannot open\n");
return NULL;
}
int rows = 0;
while(!feof(fp))
{
if(fgetc(fp) == '\n')
{
rows ++;
}
}
rows ++;
int* keys = (int*)malloc(3 * rows * sizeof(int));
fseek(fp, 0L, 0);
while(!feof(fp))
{
for(int i = 0;i < rows;i ++)
{
for(int j = 0;j < 3;j ++)
{
fscanf(fp,"%d", &keys[(3 * i) + j]);
}
}
}
fclose(fp);
return keys;
}
int main()
{
char str[20];
printf("Build_tree ");
scanf("%s",str);
int* keys = Read_file(str);
//Whatever you want to do with the keys
return 0;
}
Comment for any queries.
This program supposed to read a text and count the number of vowels and consonants. it should ignore any non alphabetic characters. the result should me something like this:
Enter your text: I have to TURN this..in before midnight!!
a, e, i, o, u, y
1, 3, 5, 2, 1, 0
There are 19 consonants.
but the result from my code is :
Enter your text: I have to TURN this..in before midnight!!
a, e, i, o, u, y
1, 3, 4, 2, 0, 0
There are 31 consonants.
I dont know what is happening!! Also this is an assignment and I have to use all these functions and I cannot add or remove them! I read couple of other ways to count and display the numbers but unfortunately the template was given...
#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
using namespace std;
// FUNCTION PROTOTYPES GO HERE:
void init_vectors(vector<char> & vowels, vector<int> & frequencies);
string read_text(const string & prompt);
bool is_alphabetic(const char character);
void create_list(const string & str_text, vector<char> & vec_text);
bool is_member(const vector<char> & list, char character);
int find_index(const vector<char> & list, char character);
int compute_vowel_freqs(const vector<char> & text, const vector<char> & vowels, vector<int> & freqs);
void display_characters(const vector<char> & characters, const int colwidth);
void display_freqs(const vector<int> & freqs, const int colwidth);
int main()
{
vector<char> vowels;
vector<int> freqs;
string input;
vector<char> text;
int consonants(0);
const int COLUMNWIDTH = 2;
init_vectors(vowels, freqs);
input=read_text("Enter your text: ");
create_list(input, text);
compute_vowel_freqs(text, vowels, freqs);
display_characters(vowels, COLUMNWIDTH);
display_freqs(freqs, COLUMNWIDTH);
consonants = compute_vowel_freqs(text, vowels, freqs);
cout<<"There are "<< consonants<< " consonants."<<endl;
return 0;
}
void init_vectors(vector<char> & vowels, vector<int> & frequencies)
{
for (int i(0); i<6; i++) //i is loop variable
{
frequencies.push_back(0);
}
vowels.push_back('a');
vowels.push_back('e');
vowels.push_back('i');
vowels.push_back('o');
vowels.push_back('u');
vowels.push_back('y');
}
string read_text(const string & prompt)
{
string phrase;
cout<<prompt;
getline(cin,phrase);
return phrase;
}
bool is_alphabetic(const char character)
{
bool alphabet;
if ((character > 'a' && character < 'z')||(character > 'A' && character < 'Z'))
{
alphabet = true;
}
return alphabet;
}
void create_list(const string & str_text, vector<char> & vec_text)
{
for( int i = 0 ; i < str_text.length() ; i++)
{
if(is_alphabetic(str_text[i]))
vec_text.push_back(str_text[i]);
}
}
bool is_member(const vector<char> & list, char character)
{
bool vowel;
for (int i(0); i<list.size(); i++)
{
if (character == list[i])
{
vowel=true;
}
}
return vowel;
}
int find_index(const vector<char> & list, char character)
{
int index = -1;
for(int i=0; i<list.size(); i++)
{
if(character == list[i])
{
index = i;
break;
}
}
return index;
}
int compute_vowel_freqs(const vector<char> & text, const vector<char> & vowels, vector<int> & freqs)
{
int num_cons(0);
for(int i = 0 ; i < text.size() ; i++)
{
int index;
if(is_member(vowels, text[i]))
{
index = find_index(vowels , tolower(text[i]));
freqs[index]++;
}
else
num_cons++;
}
return num_cons;
}
void display_characters(const vector<char> & characters, const int colwidth)
{
for(int i=0; i<characters.size(); i++)
{
cout<<setw(colwidth)<<characters[i];
if((i+1)<characters.size())
{
cout<<",";
}
}
cout<<endl;
return;
}
void display_freqs(const vector<int> & freqs, const int colwidth)
{
for(int i=0; i<freqs.size(); i++)
{
cout<<setw(colwidth)<<freqs[i];
if((i+1)<freqs.size())
cout<<",";
}
cout<<endl;
return;
}
If you write hundreds of lines of code before you test any of it, you're bound to fail. Start small and simple, add complexity a little at a time, test at every step, and never add to code that doesn't work.
You should have tested these functions one by one as you wrote them. Here's the first problem:
bool is_alphabetic(const char character)
{
bool alphabet;
if ((character > 'a' && character < 'z')||(character > 'A' && character < 'Z'))
{
alphabet = true;
}
return false;
}
This always returns false, so nothing is recognized as text.
EDIT:
Second problem: is_member has exactly the same bug, with the same solution.
EDIT:
Third problem: I failed to notice that in this line in is_alphabetic:
if ((character > 'a' && character < 'z')||(character > 'A' && character < 'Z'))
You're using '>' and '<' when you should use ">=" and "<=". According to this function, 'a' and 'z' are not letters.
Look, you're still trying to test and fix this program as a whole. You must test it piecemeal. Pick a place in main and print out every variable that should have been assigned a value by then. This function may be useful:
void printVector(const vector<char> &V)
{
for(vector<char>::const_iterator citr=V.begin(); citr!=V.end(); ++citr)
cout << *citr;
cout << endl;
}
Then inspect the results. If a variable doesn't contain what it should, then something above that point is misbehaving. Trace the problem back to a function where good things go in but something bad comes out. Fix that, then look at the output again. I can't emphasize this enough: don't try to fix everything at once.
Your is_member is always false, so no char is vowel. And it results in 0 count.
bool is_member(const vector<char> & list, char character)
{
bool vowel = false; # this fix is not obligatory, I just made code look clearer
for (int i(0); i<list.size(); i++)
{
if (character == list[i])
{
vowel=true;
}
}
return vowel; # this should be fixed
}
By the way, the same issue is in the function 'is_alphabetic'. It is always false.
as we know it in C, a string defining is,
char string[] = "Hello World";
That is OK,
But I want to use a function and at initial same up,
I tried those, For example;
char * to_string()
{
return "Hello World";
}
Or;
char * to_String(void) // Function
{
char buff[16];
sprintf(buff, "%s", "Hello World");
return buff;
}
main() // main function
{
char Initial_String[] = to_String();
}
How to make this or any idea same another way.
I find what I dont send address of char Initial_String[] to fill into. No. is there Another method.
Thanks.
When you compile this, atleast in GCC, it will give you the following warning:
b.c:9: warning: function returns address of local variable
Why? Because buff[] is a local variable of function to_string(). Its scope is only inside the function to_string(). main() does not have any access to this variable. Try making buff[] a global variable instead.
Second problem: char Initial_String[] = to_String(); cannot be assigned value in this way. to_string() returns a char pointer, hence assign the value thus:
char *Initial_String = to_String();
The code below will work:
char buff[16];
char* to_String(void) // Function
{
//char buff[16]; /*this is a local variable*/
sprintf(buff, "%s", "Hello World");
return buff;
}
int main(void) // main function
{
char *Initial_String = to_String();
printf("%s", Initial_String);
return 0;
}
Yes You are right about local buffer mismake,
But This is not my wanting,
if I edit some differently,
char buff[16];
char* to_String(void) // Function
{
//char buff[16]; /*this is a local variable*/
sprintf(buff, "%s", "Hello World");
return buff;
}
int main(void) // main function
{
char *Initial_String_1 = to_String();
char *Initial_String_2 = to_String();
char *Initial_String_3 = to_String();
printf("%s", Initial_String_1 );
printf("%s", Initial_String_2 );
printf("%s", Initial_String_3 );
in this case, all strings will be same, because They have same buffer address,
I want to open the topic little more.
struct
{
long aaa;
short bbb;
int ccc;
char ddd;
.
.
. // the list goes on
}elements;
typedef struct
{
int lengt;
int *adress;
char name[10];
}_list;
char* to_String(long variable) // Function
{
sprintf(buff, "%ld", variable);
return buff;
}
int main (void)
{
_list My_List[] = {
{ sizeof(elements.aaa), &elements.aaa , to_string( elements.aaa) },
{ sizeof(elements.bbb), &elements.bbb , to_string( elements.bbb) },
{ sizeof(elements.ccc), &elements.ccc , to_string( elements.ddd) },
.
.
. //// the list goes on
};
I do not know, Do I make myself clear.
Here, string must be filled into name array, without assigning it the address.
I may have syntax mistake. the code is not tested with compiler. the idea is for illustrative purposes only.
I am trying to find a method for The purpose.
Thanks.
I have invalid read of size in the following functions using valgrind. I'm not exactly sure why but if any of you can help me that would be greatly appreciated! From what I can tell it runs okay but there are still some errors that I'm not catching that may even deal with memory allocation and deallocation. Please help!
//alternate constructor that allows for setting of the inital value of the string
MyString::MyString(const char *message)
{
int counter(0);
while(message[counter] != '\0')
{
counter++;
}
Size = counter;
**String = new char [Size];**
for(int i=0; i < Size; i++)
String[i] = message[i];
}
istream& operator>>(istream& input, MyString& rhs)
{
char* t;
int size(256);
t = new char[size];
input.getline(t,size);
**rhs = MyString(t);**
delete [] t;
return input;
}
/*Assignment operator (=) which will copy the source string into the destination string. Note that size of the destination needs to be adjusted to be the same as the source.
*/
MyString& MyString::operator=(const MyString& rhs)
{
if(this != &rhs)
{
delete [] String;
**String = new char[rhs.Size+1];**
Size = rhs.Size;
for(int i = 0; i < Size; i++)
{
** String[i] = rhs.String[i];**
}
}
return *this;
}
Any suggestions?? (All of the problem lines have **)
One thing I see is that your copy constructor doesn't allocate space for \0 and doesn't copy it. Neither does the assignment operator.. Or, if you don't store terminating zero, then why are you looking for it?
and the two implementations differ, why the inconsistency (Size vs counter)?
"From what I can tell it runs okay" - it's called undefined behaviour, or in this case: luck - or, if you like me, and like to catch bugs: a misfortune.
I have to manage servos from a computer.
So I have to send manage messages from computer to Arduino. I need manage the number of servo and the corner. I'm thinking of sendin something like this : "1;130" (first servo and corner 130, delimeter ";").
Are there any better methods to accomplish this?
Here is my this code :
String foo = "";
void setup(){
Serial.begin(9600);
}
void loop(){
readSignalFromComp();
}
void readSignalFromComp() {
if (Serial.available() > 0)
foo = '';
while (Serial.available() > 0){
foo += Serial.read();
}
if (!foo.equals(""))
Serial.print(foo);
}
This doesn't work. What's the problem?
You can use Serial.readString() and Serial.readStringUntil() to parse
strings from Serial on arduino
You can also use Serial.parseInt() to read integer values from serial
Code Example
int x;
String str;
void loop()
{
if(Serial.available() > 0)
{
str = Serial.readStringUntil('\n');
x = Serial.parseInt();
}
}
The value to send over serial would be "my string\n5" and the result would be str = "my string" and x = 5
Note: Serial.available() inherits from the Stream utility class.
https://www.arduino.cc/reference/en/language/functions/communication/serial/available/
This is a Great sub I found. This was super helpful and I hope it will be to you as well.
This is the method that calls the sub.
String xval = getValue(myString, ':', 0);
This is The sub!
String getValue(String data, char separator, int index)
{
int found = 0;
int strIndex[] = {
0, -1 };
int maxIndex = data.length()-1;
for(int i=0; i<=maxIndex && found<=index; i++){
if(data.charAt(i)==separator || i==maxIndex){
found++;
strIndex[0] = strIndex[1]+1;
strIndex[1] = (i == maxIndex) ? i+1 : i;
}
}
return found>index ? data.substring(strIndex[0], strIndex[1]) : "";
}
Most of the other answers are either very verbose or very general, so I thought I'd give an example of how it can be done with your specific example using the Arduino libraries:
You can use the method Serial.readStringUntil to read until your delimiter from the Serial port.
And then use toInt to convert the string to an integer.
So for a full example:
void loop()
{
if (Serial.available() > 0)
{
// First read the string until the ';' in your example
// "1;130" this would read the "1" as a String
String servo_str = Serial.readStringUntil(';');
// But since we want it as an integer we parse it.
int servo = servo_str.toInt();
// We now have "130\n" left in the Serial buffer, so we read that.
// The end of line character '\n' or '\r\n' is sent over the serial
// terminal to signify the end of line, so we can read the
// remaining buffer until we find that.
String corner_str = Serial.readStringUntil('\n');
// And again parse that as an int.
int corner = corner_str.toInt();
// Do something awesome!
}
}
Of course we can simplify this a bit:
void loop()
{
if (Serial.available() > 0)
{
int servo = Serial.readStringUntil(';').toInt();
int corner = Serial.readStringUntil('\n').toInt();
// Do something awesome!
}
}
You need to build a read buffer, and calculate where your 2 fields (servo #, and corner) start and end. Then you can read them in, and convert the characters into Integers to use in the rest of your code. Something like this should work (not tested on Arduino, but standard C):
void loop()
{
int pos = 0; // position in read buffer
int servoNumber = 0; // your first field of message
int corner = 0; // second field of message
int cornerStartPos = 0; // starting offset of corner in string
char buffer[32];
// send data only when you receive data:
while (Serial.available() > 0)
{
// read the incoming byte:
char inByte = Serial.read();
// add to our read buffer
buffer[pos++] = inByte;
// check for delimiter
if (itoa(inByte) == ';')
{
cornerStartPos = pos;
buffer[pos-1] = 0;
servoNumber = atoi(buffer);
printf("Servo num: %d", servoNumber);
}
}
else
{
buffer[pos++] = 0; // delimit
corner = atoi((char*)(buffer+cornerStartPos));
printf("Corner: %d", corner);
}
}
It looks like you just need to correct
foo = ''; >>to>> foo = "";
foo += Serial.read(); >>to>> foo += char(Serial.read());
I made also shomething similar..:
void loop(){
while (myExp == "") {
myExp = myReadSerialStr();
delay(100);
}
}
String myReadSerialStr() {
String str = "";
while (Serial.available () > 0) {
str += char(Serial.read ());
}
return str;
}
This code reads string until it sees '>' character
void loop() {
// put your main code here, to run repeatedly:
String msg = getMessage();
}
String getMessage() {
String msg = "";
while (Serial.available()>0) {
msg = Serial.readStringUntil('>');
}
return msg;
}
It's universal parser
struct servo
{
int iServoID;
int iAngle;
};
std::vector<std::string> split(const std::string& str, const std::string& delim)
{
std::vector<std::string> tokens;
size_t prev = 0, pos = 0;
do
{
pos = str.find(delim, prev);
if (pos == std::string::npos) pos = str.length();
std::string token = str.substr(prev, pos-prev);
if (!token.empty()) tokens.push_back(token);
prev = pos + delim.length();
}
while (pos < str.length() && prev < str.length());
return tokens;
}
std::vector<servo> getServoValues(const std::string& message)
{
std::vector<servo> servoList;
servo servoValue;
std::vector<std::string> servoString;
std::vector<std::string> values = split(message, ",");
for (const auto& v : values)
{
servoString.clear();
servoString = split(v, ";");
servoValue.iServoID = atoi(servoString[0].c_str()); //servoString[0].toInt();
servoValue.iAngle = atoi(servoString[1].c_str());// servoString[1].toInt();
servoList.emplace_back(servoValue);
}
return servoList;
}
to call:
std::string str = "1;233,2;123";
std::vector<servo> servos = getServoValues(str);
for (const auto & a : servos)
std::cout<<a.iServoID << " " << a.iAngle << std::endl;
Result
1 233
2 123