whats the best way of creating a 'const char*' using available variables? For example, a function requires a const char* as a parameter to locate a file i.e. "invader1.png". If I have 5 different invader images, how can I iterate from 1:5 so "Invader1.png".."Invader2.png..etc etc
so i want "invader" + %d + ".png"
i tried sprintf and casting but to no avail.
I hope my description makes sense, thanks
update with code:
for (int y=0; y<250; y+=50){
stringstream ss;
ss << "invader" << (y/50) << ".png";
const char* rr = ss.str().c_str();
printf("%s", rr);
for (int x=0; x<550;x+=50){
Invader inv(rr, x+50, y+550, 15, 15, 1, false, (y/50 + 50));
invaders[i] = inv;
i++;
}
}
Use std::stringstream. Something like this:
std::stringstream ss;
ss << "invader" << my_int << ".png";
my_func(ss.str().c_str());
Since you're using C++, you can simply use std::string and then use the c_str() function to get a const char* which you can pass to the function. One simple way to construct such strings is to use std::ostringstream from <sstream>:
for (int i = 1; i <= 5; ++i) {
std::ostringstream ss;
ss << "invader" << i << ".png";
foo(ss.str().c_str()); // where foo is the specified function
}
You could also use sprintf() and a character array, but then you need to pay attention to things like the size of the buffer. For the sake of completeness, here's how to do the same with sprintf, but I suggest you go with the std::string approach, which is more C++-like:
for (int i = 1; i <= 5; ++i) {
char buf[13]; // big enough to hold the wanted string
std::ostringstream ss;
sprintf(buf, "invader%d.png", i);
foo(buf); // where foo is the specified function
}
Then i would guess your looking to cast an int variable to char, so you can iterate through your invader%d.png files.
Have you tried itoa function ?
http://www.cplusplus.com/reference/clibrary/cstdlib/itoa/
Related
I got an issue with sprintf buffer.
As you can see in the code down below I'm saving with sprintf a char array to the buffer, so pFile can check if there's a file named like that in the folder. If it's found, the buffer value will be assigned to timecycles[numCycles], and numCycles will be increased. Example: timecycles[0] = "timecyc1.dat". It works well, and as you can see in the console output it recognizes that there are only timecyc1.dat and timecyc5.dat in the folder. But as long as I want to read timecycles with a for loop, both indexes have the value "timecyc9.dat", eventhough it should be "timecyc1.dat" for timecycles[0] and "timecyc5.dat" for timecycles1. Second thing is, how can I write the code so readTimecycles() returns char* timecycles, and I could just initialize it in the main function with char* timecycles[9] = readTimecycles() or anything like that?
Console output
#include <iostream>
#include <cstdio>
char* timecycles[9];
void readTimecycles()
{
char buffer[256];
int numCycles = 0;
FILE* pFile = NULL;
for (int i = 1; i < 10; i++)
{
sprintf(buffer, "timecyc%d.dat", i);
pFile = fopen(buffer, "r");
if (pFile != NULL)
{
timecycles[numCycles] = buffer;
numCycles++;
std::cout << buffer << std::endl; //to see if the buffer is correct
}
}
for (int i = 0; i < numCycles; i++)
{
std::cout << timecycles[i] << std::endl; //here's the issue with timecyc9.dat
}
}
int main()
{
readTimecycles();
return 0;
}
With the assignment
timecycles[numCycles] = buffer;
you make all pointers point to the same buffer, since you only have a single buffer.
Since you're programming in C++ you could easily solve your problem by using std::string instead.
If I would remake your code into something a little-more C++-ish and less C-ish, it could look something like
std::array<std::string, 9> readTimeCycles()
{
std::array<std::string, 9> timecycles;
for (size_t i = 0; i < timecycles.size(); ++i)
{
// Format the file-name
std::string filename = "timecyc" + std::to_string(i + 1) + ".dat";
std::ifstream file(filename);
if (file)
{
// File was opened okay
timecycles[i] = filename;
}
}
return timecycles;
}
References:
std::array
std::string
std::to_string
std::ifstream
The fundamental problem is that your notion of a string doesn't match what a 'char array' is in C++. In particular you think that because you assign timecycles[numCycles] = buffer; somehow the chars of the char array are copied. But in C++ all that is being copied is a pointer, so timecycles ends up with multiple pointers to the same buffer. And that's not to mention the problem you will have that when you exit the readTimecycles function. At that point you will have multiple pointers to a buffer which no longer exists as it gets destroyed when you exit the readTimecycles function.
The way to fix this is to use C++ code that does match your expectations. In particular a std::string will copy in the way you expect it to. Here's how you can change your code to use std::string
#include <string>
std::string timecycles[9];
timecycles[numCycles] = buffer; // now this really does copy a string
I want to delete images from a file, the images are named: "1.jpg, 2.jpg ....", i have tried the code above but it gives me this error: no matching function for call to 'remove(std::__cxx11::string&)'
int i;
for (i=0;i<frame;i++)//frame contain the number of images i want to delete
{
std::stringstream ss;
ss << i;
std::string str = ss.str();
const char *cstr = str.c_str();
str=str+".jpg";
remove(str);
}
If someone can help thank you in advence.
You almost have it. remove requires a const char*, not a std::string. That means you need
remove(str.c_str());
We can also get rid of the stringstream and use std::to_string instead in something like
for (i=0; i<frame; i++)
{
const std::string str = to_string(i) + ".jpg";
remove(str.c_str());
}
I don't know whether or not this is possible but I have used this technique in different languages but am struggling to use it in C++. I have 10 images that I am trying to load into an array using a loop as so:
for (int i = 0; i < 10; i++)
{
Sprite[i] = IMG_LoadTexture(renderer, "Graphics/Player" + i + ".png");
}
This however does not seem to work in C++ so I was wondering what I am doing wrong, or what can I do to get the same result without having to load each image individually like so:
Sprite[0] = IMG_LoadTexture(renderer, "Graphics/Player0.png");
My error is: "Expression must have integral or unscoped enum type"
Thanks for any help =)
You cannot do this:
"This is my number: " + (int)4 + "!";
This is illegal. It will give you an error for trying to operator+ a const char* and a const char[SOME_INT_GOES_HERE] or another error for trying to use operator+ to add an int onto a string. Things just don't work that way.
You'd either have to use C (i.e. snprintf()) or a string stream. Here's my test code for isolating your problem:
#include <iostream>
#include <string>
int main()
{
int a = 1;
std::string str = "blah";
std::string end = "!";
//std::string hello = str + a + end;// GIVES AN ERROR for operator+
std::string hello = "blah" + a + "!";
//const char* c_str = "blah" + a + "end";
//std::cout << c_str << std::endl;
std::cout << hello << std::endl;
return 0;
}
Here's an alternative solution using string streams.
#include <iostream>
#include <string>
#include <sstream>
int main()
{
int i = 0;
std::string str;
std::stringstream ss;
while (i < 10)
{
//Send text to string stream.
ss << "text" << i;
//Set string to the text inside string stream
str = ss.str();
//Print out the string
std::cout << str << std::endl;
//ss.clear() doesn't work. Calling a constructor
//for std::string() and setting ss.str(std::string())
//will set the string stream to an empty string.
ss.str(std::string());
//Remember to increment the variable inside of while{}
++i;
}
}
Alternatively, you can also use std::to_string() if you're using C++11 (which just requires -std=c++11) but std::to_string() is broken on some sets of compilers (i.e. regular MinGW). Either switch to another flavor where it works (i.e. MinGW-w64) or just write your own to_string() function using string streams behind the scenes.
snprintf() may be the fastest way of doing such a thing, but for safer C++ and better style, it is recommended you use a non-C way of doing things.
I had a similar problem and I solwed it this way:
#include <iostream>
using namespace std;
int main() {
string line;
for (int i = 0; i < 10; i++) {
line = "Graphics/Player" + inttostr(i) + ".png"; //I wrote inttostr function because built in inttostr functions messed up my program (see below)
char charger[line.length()]; //creating char array
for (int i = 0; i < sizeof(line); i++) {
charger[i] = line[i]; // copying string to char arry
}
Sprite[i] = IMG_LoadTexture(renderer, charger);
}
}
string inttostr(int integer) { //I know it isn't the best way to convert integer to string, but it works
string charakter;
int swap;
bool negativ = false;
if (integer < 0) {
integer = -integer;
negativ = true;
}
if (integer == 0) {
charakter = "0";
}
while (integer >= 1) {
swap = integer % 10;
integer = integer / 10;
charakter = char(swap + 48) + charakter;
}
if (negativ) {
charakter = "-" + charakter;
}
return charakter;
}
So I am working on a tool that dereferences the values of some addresses, it is in both C and C++, and although I am not familiar with C++ I figured out I can maybe take advantage of the string type offered by C++.
What I have is this:
unsigned char contents_address = 0;
unsigned char * address = (unsigned char *) add.addr;
int i;
for(i = 0; i < bytesize; i++){ //bytesize can be anything from 1 to whatever
if(add.num == 3){
contents_address = *(address + i);
//printf("%02x ", contents_address);
}
}
As you can see what I am trying to do is dereference the unsigned char pointer. What I want to do is have a string variable and concatenate all of the dereferenced values into it and by the end instead of having to go through a for case for getting each one of the elements (by having an array of characters or by just going through the pointers) to have a string variable with everything inside.
NOTE: I need to do this because the string variable is going to a MySQL database and it would be a pain to insert an array into a table...
Try this that I borrowed from this link:
http://www.corsix.org/content/algorithmic-stdstring-creation
#include <sstream>
#include <iomanip>
std::string hexifyChar(int c)
{
std::stringstream ss;
ss << std::hex << std::setw(2) << std::setfill('0') << c;
return ss.str();
}
std::string hexify(const char* base, size_t len)
{
std::stringstream ss;
for(size_t i = 0; i < len; ++i)
ss << hexifyChar(base[i]);
return ss.str();
}
I didn't quite understand what you want to do here (why do you assign a dereferenced value to a variable called ..._address)?.
But maybe what you're looking for is a stringstream.
Here's a relatively efficient version that performs only one allocation and no additional function calls:
#include <string>
std::string hexify(unsigned char buf, unsigned int len)
{
std::string result;
result.reserve(2 * len);
static char const alphabet[] = "0123456789ABCDEF";
for (unsigned int i = 0; i != len)
{
result.push_back(alphabet[buf[i] / 16]);
result.push_back(alphabet[buf[i] % 16]);
{
return result;
}
This should be rather more efficient than using iostreams. You can also modify this trivially to write into a given output buffer, if you prefer a C version which leaves allocation to the consumer.
I'm trying to write a code which stores strings in an array. I'm trying to do it with char* but I couldn't achieve. I search the net but couldn't find an answer. I've tried the code below, but it didn't compile.I use string stream because at some point I need to concatenate a string with an integer.
stringstream asd;
asd<<"my name is"<<5;
string s = asd.str();
char *s1 = s;
> I'm trying to write a code which stores strings in an array.
Well, first you'll need an arary of strings. I don't like using naked arrays, so I use std::vector:
std::vector<std::string> myStrings;
But, I understand you have to use an array, so we'll use an array instead:
// I hope 20 is enough, but not too many.
std::string myStrings[20];
int j = 0;
> I use string stream because ...
Okay, we'll use stringstream:
std::stringstream s;
s << "Hello, Agent " << 99;
//myStrings.push_back(s.str()); // How *I* would have done it.
myStrings[j++] = s.str(); // How *you* have to do it.
That gets us one string, but you want an array of them:
for(int i = 3; i < 11; i+=2) {
s.str(""); // clear out old value
s << i << " is a" << (i==9?" very ":"n ") << "odd prime.";
//myStrings.push_back(s.str());
myStrings[j++] = s.str();
}
Now you have an array of strings.
Complete, tested program:
#include <sstream>
#include <iostream>
int main () {
// I hope 20 is enough, but not too many.
std::string myStrings[20];
int j = 0;
std::stringstream s;
s << "Hello, Agent " << 99;
//myStrings.push_back(s.str()); // How *I* would have done it.
myStrings[j++] = s.str(); // How *you* have to do it.
for(int i = 3; i < 11; i+=2) {
s.str(""); // clear out old value
s << i << " is a" << (i==9?" very ":"n ") << "odd prime.";
//myStrings.push_back(s.str());
myStrings[j++] = s.str();
}
// Now we have an array of strings, what to do with them?
// Let's print them.
for(j = 0; j < 5; j++) {
std::cout << myStrings[j] << "\n";
}
}
How about something like this?
vector<string> string_array;
stringstream asd;
asd<<"my name is"<<5;
string_array.push_back(asd.str());
char *s1 = s;
Is illegal. You either need:
const char *s1 = s.c_str();
if you're not set on char*, or you'll need to allocate a new char* and use strcpy to copy the contents from the string.
Just change your code to
char const* s1 = s.c_str();
because a pointer to char can't store a string object, only a pointer to char, which is what c_str() returns.
I wouldn't use the char * directly. I would wrap it in something like the template below. You can override the operators you need to do any more operations (example, I would make data a private member, and override the operators to make the data print out cleanly). I did the assignment operator just to demonstrate how clean that could make code.
#include "MainWindow.h"
#include <stdio.h>
using namespace std;
template<size_t size>
class SaferChar
{
public:
SaferChar & operator=(string const & other)
{
strncpy(data, other.c_str(), size);
return *this;
}
char data[size];
};
int main(int argc, char *argv[])
{
SaferChar<10> safeChar;
std::string String("Testing");
safeChar = String.c_str();
printf("%s\n", safeChar.data);
return 0;
}