C / C++ / MFC

1-Jul-08 1:42

How do I convert from std::string to char* in C++?

toxcct1-Jul-08 1:53

1-Jul-08 1:53

std::string s = "Hello World";
 
char* psz = s.c_str();

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T.RATHA KRISHNAN1-Jul-08 2:07

1-Jul-08 2:07

I followed the same method. But the following code:

    std::string path = dtCore::GetDeltaRootPath();
const char* exeroot = path.c_str();
strcat(path,"/");
strcat(path,"CharacterAnimation.exe");
result = system(path);
return true;

gives me the following errors:
error C2664: 'strcat' : cannot convert parameter 1 from 'std::string' to 'char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
.\GUI.cpp(195) : error C2664: 'strcat' : cannot convert parameter 1 from 'std::string' to 'char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
.\GUI.cpp(196) : error C2664: 'system' : cannot convert parameter 1 from 'std::string' to 'const char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

How do I resolve?

toxcct1-Jul-08 2:19

1-Jul-08 2:19

why are you using path instead of exeroot you just allocated ?

it's obvious you don't read error messages, or you don't understand what you're doing...
check your code again.

std::string path = dtCore::GetDeltaRootPath();
const char* exeroot = path.c_str();
strcat(exeroot, "/");
strcat(exeroot, "CharacterAnimation.exe");
result = <font color="red">system</font>(exeroot);
return <font color="red">true</font>;

BTW, you seem not to have takenn in account my previous remarks...

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T.RATHA KRISHNAN1-Jul-08 2:25

1-Jul-08 2:25

Now this line shows:

char* exeroot = path.c_str();

the following error.
error C2440: 'initializing' : cannot convert from 'const char *' to 'char *'

toxcct1-Jul-08 2:43

1-Jul-08 2:43

T.RATHA KRISHNAN wrote:
char* exeroot = path.c_str();

add const then, as std::string::c_str() returns const char*

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CPallini1-Jul-08 2:27

1-Jul-08 2:27

I think you'll get buffer overruns that way.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Stephen Hewitt1-Jul-08 14:34

Stephen Hewitt

1-Jul-08 14:34

That's assuming you cast away the consts so it even compiles.

Steve

CPallini1-Jul-08 21:26

1-Jul-08 21:26

Good point indeed.
Smile | :)

Stephen Hewitt1-Jul-08 14:33

Stephen Hewitt

1-Jul-08 14:33

toxcct wrote:
const char* exeroot = path.c_str();
strcat(exeroot, "/");
strcat(exeroot, "CharacterAnimation.exe");

Bad advice. The buffer returned from c_str is const and thus can't be modified. And it's wrong to cast away the const as it's const for a reason: the buffer used by a std::string need not be contiguous memory. If this is the case calling c_str makes a temporary buffer and copies the non-contiguous memory blocks into one contiguous memory block for you. It is not required to copy the blocks back. Also your code is in serious danger of causing a buffer overrun (if you made it compile by casting away the const): how do you know how big the buffer is?

Anyway the correct way is simpler, safe, works, is portable and requires no casts:

std::string path = dtCore::GetDeltaRootPath();
path += "/CharacterAnimation.exe";
system(path.c_str());

Steve

killabyte1-Jul-08 2:20

killabyte

1-Jul-08 2:20

You are sending strcat() the wrong param type i think.

std::string path = dtCore::GetDeltaRootPath();
const char* exeroot = path.c_str();
char* StrToCat = path.c_str();

strcat(StrToCat,"/");
strcat(StrToCat,","CharacterAnimation.exe");

etc..

CPallini1-Jul-08 2:29

1-Jul-08 2:29

Buffer overrun along the horizon.
Smile | :)

killabyte1-Jul-08 2:34

killabyte

1-Jul-08 2:34

absolutely, but i only meant to identify the problem a lil more clearly Frown | :(

Stephen Hewitt1-Jul-08 14:42

Stephen Hewitt

1-Jul-08 14:42

This is seriously wrong. See http://www.codeproject.com/script/Forums/View.aspx?fid=1647&msg=2620460[^] for details.

Steve

CPallini1-Jul-08 2:24

1-Jul-08 2:24

T.RATHA KRISHNAN wrote:
I followed the same method. But the following code:

Nope. You got it wrongly.

T.RATHA KRISHNAN wrote:
std::string path = dtCore::GetDeltaRootPath();
const char* exeroot = path.c_str();
strcat(path,"/");
strcat(path,"CharacterAnimation.exe");
result = system(path);
return true;

change to

std::string path = dtCore::GetDeltaRootPath();
path +="/";
path +="CharacterAnimation.exe";
result = system(path.c_str());
return true;

T.RATHA KRISHNAN1-Jul-08 2:39

1-Jul-08 2:39

Thanks a lot. I resolved the errors. But now my problem is: the variable path contains "Program Files". Compiler takes only Program leaving the space and after that. So the console displays an error: "C:\Program" is not recognized as an internal or external command,operable program or batch file. What to do?

toxcct1-Jul-08 2:46

1-Jul-08 2:46

F*CK, you don't listen to me.

if you were using ShellExecute, that wouldn't have happened.
use quotes ( " " ) around your string (within the string I mean), or use ShellExecute

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T.RATHA KRISHNAN1-Jul-08 2:54

1-Jul-08 2:54

I don't understand this:(with in the string). My string definition is:

path += "/";
  path += "CharacterAnimation.exe";
  result = system(path.c_str());

Where should I put double quotes?

toxcct1-Jul-08 2:58

1-Jul-08 2:58

god, do you understand this : use ShellExecute ?????
::ShellExecuteA(NULL, "open", path.c_str(), NULL, NULL, SW_NORMAL);

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SandipG 1-Jul-08 3:11

SandipG

1-Jul-08 3:11

Regards,
Sandip.

T.RATHA KRISHNAN1-Jul-08 3:20

1-Jul-08 3:20

Thanks. It's working now.

toxcct1-Jul-08 3:22

1-Jul-08 3:22

T.RATHA KRISHNAN wrote:
Thanks. It's working now

at last... glad to hear that

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