Help Converting String to Char* - GameCreators Forum

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fubarpk

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Posted: 30th Aug 2006 11:25

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I have been researching code on forums and i want to convert a float to a char* so as i can use dbPrint()
I found this code for converting to a string using namespace which i plan on using

+ Code Snippet

string toString(float num) {
	ostringstream myStream;
	myStream << num;
	return myStream.str();
}

But i really need a way of converting that to a char* any help would be greatly appreciated.

Below is code i wush to use it in

+ Code Snippet

#include "DarkGDK.h";
#include <string.h>
#include <stdlib.h>
#include <sstream>
#include "math.h";
using namespace std;
string toString(float num);

void DarkGDK ( void ){ 
int PDist;
float power;
char *MyChar;
while (PDist>0.0f)
{
MyChar=dbInput();
PDist=atoi(MyChar);
power = (PDist/(sqrt(PDist)*(500)));//+rnd(200)));//*500.00);//*(500.00+rnd(200)))
//*MyChar sendto  toString(power);
dbPrint(MyChar);
}
}
// returns the string representation of a number
string toString(float num) {
	ostringstream myStream;
	myStream << num;
	return myStream.str();
}

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OSX Using Happy Dude

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Posted: 30th Aug 2006 12:10

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Whats wrong with using sprintf or even sprintf_s ? Or does it have to belong to the almight STD class ?

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IanM

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Posted: 30th Aug 2006 16:01

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Slowest to fastest:

std::stringstream
sprintf
_ecvt (or one of it's partner functions, microsoft only)

Easiest to hardest:

sprintf
std::stringstream
_ecvt

If you only need to use ints, then the same applies, except use itoa instead of _ecvt

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fubarpk

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Posted: 30th Aug 2006 16:34

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so far i have this code but it only returns 0

+ Code Snippet

char* toString(float num) {
	char myChar[100];
	ostringstream myStream;
	string cpp_string;
	
	myStream << num;
	cpp_string=myStream.str();
	strncpy(myChar,cpp_string.c_str(),sizeof(myChar));
	//return myStream.str()
	return myChar;
}

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fubarpk

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Posted: 30th Aug 2006 16:46

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heres the complete code still not working incase you want to see what the includes etc are it returns 0 to the dbPrint function

+ Code Snippet

#include "DarkGDK.h";
#include <stdio.h>;
#include <string>;
#include <stdlib.h>;
#include <sstream>;
#include "math.h";
using namespace std;
char* toString(float num);

void DarkGDK ( void ){ 
int PDist=1;
float power;
char *MyChar;
while (PDist>0.0f)
{
MyChar=dbInput();
PDist=atoi(MyChar);
power = (PDist/(dbSQRT(PDist)*(500)));//+rnd(200)));//*500.00);//*(500.00+rnd(200)))
//*MyChar sendto  toString(power);
dbPrint(toString(power));
}
}
char* toString(float num) {
	char myChar[100];
	ostringstream myStream;
	string cpp_string;
	
	myStream << num;
	cpp_string=myStream.str();
	strncpy(myChar,cpp_string.c_str(),sizeof(myChar));
	//return myStream.str()
	return myChar;
}

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Miguel Melo

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Posted: 30th Aug 2006 20:04

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That's not gonna work. If for nothing else, because you are returning myChar, which is allocatted in the stack, and which will most likely be blown away when the toString() function call returns.

It certainly will be overwritten next time you call any other function from wherever toString has just been called...

I have vague plans for World Domination

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fubarpk

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Posted: 31st Aug 2006 14:41

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This code works perfectly

<b>Extra</b>:if you get rid of the leftprecfunc and remove comment on the define leftprec it can be made for doubles etc but yu overload the pow function in math.h which i cant figure how to set it with a define but can overload as function by prefixing with type ie int in this case.

#include "DarkGDK.h";
#include <stdio.h>;
#include <string>;
#include <stdlib.h>;
#include <sstream>;
#include <iostream>;
#include "math.h";
//#define leftprec(x,y) (x - (((int)floor(x) - (((int)floor(x))% ((int)(pow(10,y)))))))
using namespace std;
float leftprec(float x,float y);
char* toString(float num);

void DarkGDK ( void ){ 
int PDist=1;
float power;
char *MyChar;
while (PDist>0.0f)
{
MyChar=dbInput();
PDist=atoi(MyChar);
power = (PDist/((float)sqrt((float)PDist)*(11.231f+(dbRND(2)))));//*500.00);//*(500.00+rnd(200)))
//power=(100/(dbSQRT(100)*(500)));
//*MyChar sendto  toString(power);
dbPrint(toString(power));
}
}

// returns the string representation of a number
char* toString(float num) {
	char myChar[20];
	ostringstream myStream;
	string cpp_string;
	
	//myStream << num;
	//myStream<<num<<endl;
	myStream<<leftprec(num,1)<<endl;
	cpp_string=myStream.str();
	strncpy(myChar,cpp_string.c_str(),sizeof(myChar));
	myStream.str("");
	//return myStream.str()
	return myChar;
}
float leftprec(float x,float y) 
{return(x - (((int)floor(x) - (((int)floor(x))% ((int)(pow(10,y)))))));
}

+ Code Snippet

#include "DarkGDK.h";
#include <stdio.h>;
#include <string>;
#include <stdlib.h>;
#include <sstream>;
#include <iostream>;
#include "math.h";
//#define leftprec(x,y) (x - (((int)floor(x) - (((int)floor(x))% ((int)(pow(10,y)))))))
using namespace std;
float leftprec(float x,float y);
char* toString(float num);

void DarkGDK ( void ){ 
int PDist=1;
float power;
char *MyChar;
while (PDist>0.0f)
{
MyChar=dbInput();
PDist=atoi(MyChar);
power = (PDist/((float)sqrt((float)PDist)*(11.231f+(dbRND(2)))));//*500.00);//*(500.00+rnd(200)))
//power=(100/(dbSQRT(100)*(500)));
//*MyChar sendto  toString(power);
dbPrint(toString(power));
}
}

// returns the string representation of a number
char* toString(float num) {
	char myChar[20];
	ostringstream myStream;
	string cpp_string;
	
	//myStream << num;
	//myStream<<num<<endl;
	myStream<<leftprec(num,1)<<endl;
	cpp_string=myStream.str();
	strncpy(myChar,cpp_string.c_str(),sizeof(myChar));
	myStream.str("");
	//return myStream.str()
	return myChar;
}
float leftprec(float x,float y) 
{return(x - (((int)floor(x) - (((int)floor(x))% ((int)(pow(10,y)))))));
}

fubar

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IanM

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Posted: 1st Sep 2006 00:36

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If it works, then it's more by luck than judgement.

Your array is allocated on the stack. The stack is used to store parameters, local variables, return addresses etc, and every time you call a new function there is a good chance that your array contents will be overwritten.

Making this:

+ Code Snippet

char myChar[20];

into this:

+ Code Snippet

static char myChar[20];

is marginally better in that it won't get overwritten by calling new functions, but it means that you lose the old value every time you call the function again.

Making the function either write to an array area that has been passed as a parameter, or passing back an object containing the string is a much better and safer way of doing it.

+ Code Snippet

#include "DarkGDK.h";
#include <stdio.h>;
#include <string>;
#include <stdlib.h>;
#include <sstream>;
#include <iostream>;
#include "math.h";
//#define leftprec(x,y) (x - (((int)floor(x) - (((int)floor(x))% ((int)(pow(10,y)))))))
using namespace std;
float leftprec(float x,float y);
char* toString(float num);

void DarkGDK ( void ){ 
	int PDist=1;
	float power;
	char *MyChar;
	while (PDist>0.0f)
	{
		MyChar=dbInput();
		PDist=atoi(MyChar);
		power = (PDist/((float)sqrt((float)PDist)*(11.231f+(dbRND(2)))));//*500.00);//*(500.00+rnd(200)))
		//power=(100/(dbSQRT(100)*(500)));
		//*MyChar sendto  toString(power);
		dbPrint( (char*)(toString(power).c_str()) );
	}
}

// returns the string representation of a number
string toString(float num) {
	ostringstream myStream;

	myStream<<leftprec(num,1)<<endl;
	return myStream.str();
}
float leftprec(float x,float y) 
{
	return(x - (((int)floor(x) - (((int)floor(x))% ((int)(pow(10,y)))))));
}

When are TCG gonna make these darned functions accept const char *

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fubarpk

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Posted: 4th Sep 2006 04:15

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Thanks Ian, atleast i was kinda close i had allsorts of problems doing this like overloaded function calls and incorrect redirection using .c_str() etc being unfamilar with the commands but now i have a solution above this post i hope it will help many others too.

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Dark GDK / Help Converting String to Char*