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Well if your string is exactly 4 characters you can use a cast like you did in your code sample but this is the only case that it would reliably work...
John
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Do you have any other ways that I can spin through an array and for each element in it do something different depending on the name??
steven
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Why can't you use a string compare function and put the actual strings in if statements instead of a big switch statement.
John
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This "char Names[50];" is an array of characters not strings/names. If if was a list of known names then you could use "if else" as follows:
if( !strcmp(Names[i],"some name" )
else if( !strcmp(Names[i],"some other name" )
This is 'C' code; in both 'C' and 'C++' there are more complicated, to start with, yet easier to maintain methods of accomplishing your goal.
INTP
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I know I am asking why you are doing something rather than just answering your question so I apologize.
First, there is a way to get the numeric value of a char. Just cast the char as an int and there you go.
Second, there is no numeric value of a string so you can't do what you are asking.
In your sample code, you show:
char Names[50]
for(int i=0; i<50; i++)
{
int temp = (int)Names[i]; // reinitialization error?
if(temp = the number value of 'pla')
then do some stuff;
if(temp = the number value of 'oct'0)
then do some more stuff;
}
Where is your switch statement?
Are you simulating the switch with the if statements?
In the sample shown, you have a single name which can be up to 50 chars long. You are merely comparing 1 letter from that same name at a time. If you need 50 names, you'll need to define a 2 dimensional array like char Names[50][30];
If you absolutely have to use a switch statement (like a school project) you can create a struct which contains a key value and when you populate the struct you can increment the key.
struct NameStruct
{
char Names[50][30];
int key;
};
Then you can use the NameStruct.key value in your switch statement and access the names with NameStruct.Names[key]
If your end goal is to be able to loop through an array of strings and take a different action for each string you could try:
char Names[50][MAX_NAME_LENGTH];
int x;
for (x = 0; x < MAX_NAME_LENGTH; x++)
{
if(!strcmp(Names[x], "Text to compare"))
DoSomething();
if(!strcmp(Names[x], "Other text to compare"))
DoSomethingElse();
........
if(!strcmp(Names[x], "Last text to compare"))
DoSomethingEtirelyDifferent();
}
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for (x = 0; x < MAX_NAME_LENGTH; x++)
Should be
for (x = 0; x < 50; x++)
and you should use the 'if else' construct to avoid unneeded calls to strcmp().
INTP
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John R. Shaw wrote:
for (x = 0; x < MAX_NAME_LENGTH; x++)
Should be
for (x = 0; x < 50; x++)
and you should use the 'if else' construct to avoid unneeded calls to strcmp().
 You are correct of course. Thank you!
I'm going to live forever or die trying!
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Believe me I don't have to do this for a school project.
I have created a tool that display flight simulator data in real time.
Long story short:
(this is just another feature of the program)
The flight simulator writes to a file and I use the getline() function to get the names of signals that the sim wrote and put them in TSimHeader_arr[0].Name[i] which is an array in a struct.
anyways I think the function (char)strdup(name.c_str())isn't putting them in the char array correctly.
Because when I read them bach out they are strange characters.
I don't know how to do this.
Does anyone???
steven
void setInitialValues(){<br />
sSignal.SimWriteFlag=1; <br />
sSignal.DisplayReadFlag=0; <br />
sHeader.SimStatus=setSimStatus();<br />
<br />
string name,unit,min,max,value;<br />
<br />
for(int i=0; i<sizeof(sHeader.Name); i++){<br />
getline(fin, name, ',');<br />
<br />
if(name == "STOP")<br />
break;<br />
getline(fin, unit, ',');<br />
getline(fin, min, ',');<br />
getline(fin, max, ',');<br />
getline(fin, value);<br />
<br />
TSimHeader_arr[0].Name[i] = (char)strdup(name.c_str()); <br />
TSimHeader_arr[0].Unit[i] = (char)strdup(unit.c_str()); <br />
TSimHeader_arr[0].Min[i] = atof(min.c_str());<br />
TSimHeader_arr[0].Max[i] = atof(max.c_str());<br />
TSimSignal_arr[0].Value[i] = atof(value.c_str());<br />
<br />
<br />
<br />
sig_count ++;<br />
<br />
}<br />
<br />
TSimHeader_arr[0].SignalCount = sig_count;<br />
<br />
writeRfmData();<br />
createRandNum();<br />
}
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Prototype: char *_strdup( const char *strSource );
Bad: (char)strdup(name.c_str()); // this is incorrect usage
Good: strdup(name.c_str()); // normal usage
Ok: (char*)strdup(name.c_str()); // this is redundant
INTP
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If it's a simple piece of work you want to do for each item, just use a chain of if statements using strcmp() to compare.
If it's harder (which I assume it is since you've got 50 entries in your table), define a function pointer type:
typedef int (PFNTASK*)(
const char* szName,
);
int DoPla( const char* szName, );
int DoOct( const char* szName, );Then define a structure:
typedef struct
{
const char* szName;
PFNTASK pfnTask;
} TaskEntry;Now define your array:
TaskEntry namesAndTasks[] =
{
{ "pla", DoPla },
{ "oct", DoOct }
};Finally, search for the operation to perform:
for( int iTask = 0; iTask < 50; ++i )
{
if ( strcmp(
temp,
namesAndTasks[iTask].szName
) == 0 )
{
namesAndTasks.pfnTask( temp, );
break;
}
}Usually quite effective. I prefer it to a long switch statement, even when I have sequential integer codes to switch on.
Because the code size is smaller, this can sometimes run faster than a huge switch statement too.
--
Mike Dimmick
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Mike Dimmick wrote:
Usually quite effective. I prefer it to a long switch statement, even when I have sequential integer codes to switch on.
Because the code size is smaller, this can sometimes run faster than a huge switch statement too.
Actually, most modern compilers (and this includes VC) translate switch statements on large numbers of integer variables to jump tables.
On C#, switches on strings are allowed, and above a certain threshold the compiler generates a Hashtable with jump locations and the strings as a key.
ORACLE One Real A$#h%le Called Lary Ellison
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I'm sure they do. I meant from a code maintenance point of view: it's a lot easier to maintain (I think) a set of moderately simple functions than it is to maintain a 500-line function with a huge switch statement in it.
Of course, you can still code the dispatching mechanism like:
switch ( iValue )
{
case 0:
HandleCase0();
break;
case 1:
HandleCase1();
break;
default:
assert( !"Error in case statement!" );
break;
}but that gets very boring, very quickly. Unless there was some clear profiling indication that the table version was too slow for a given code path, I'd stick to that.
As for how common libraries implement it: in Win32 programming, you typically write a big switch statement. MFC's message maps are table-based (complicated somewhat by supporting ranges). ATL's BEGIN_MSG_MAP family of macros mask a honking great if/else if chain.
The hash table implementation is probably nicer if you have a fixed set and can calculate it all in advance, and either know that you can't get false-positives or check that there's a match before you jump. For general, intelligible coding, I use the array. The threshold is obviously  because the hash table has an overhead in the hash function and the extra check in any case.
MFC has, IIRC, a small hash table for each class with a message map which contains the most recently used message map entries, so it doesn't have to search the whole table (and potentially the base class's table, and its base class, and so on down) every time a common message arrives.
My solution does require that all your operations will take the same parameters. This ain't necessarily so. One of my implementations was for a varargs function where you had command identifiers, and each command could take 0, 1 or 2 parameters. So I had to have a parameter count field as part of my jump table structure which indicated what you needed to cast the function pointer to. Again, MFC does something similar for its message maps.
--
Mike Dimmick
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Mike Dimmick wrote:
but that gets very boring, very quickly. Unless there was some clear profiling indication that the table version was too slow for a given code path, I'd stick to that.
I agree. Actually, everytime I see a huge switch statement (as I'm an OOP die-hard) I start to ask what's wrong with the design, since this should be solved by a virtual method call. Not all switches should be virtual calls, but normally they indicate some design flaw in an OOP world.
ORACLE One Real A$#h%le Called Lary Ellison
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Generally I'd agree, but in the case where you'd basically need an object for each 'arm' of the switch statement which you wouldn't use anywhere else, it's wasteful of programming time. The virtual method case is generally more maintainable, sure.
Of course you may well need some kind of factory method or object to create the objects, so you're either back to the switch statement again, or some other kind of creation table.
Languages with reflection can of course use the name of the class in order to create one; the advantage that MFC's Run-time Class Information has over the C++ language's standard RTTI is that you can (if your class uses DECLARE_DYNCREATE or DECLARE_SERIAL) perform dynamic creation through the RUNTIME_CLASS macro.
--
Mike Dimmick
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/* ATOF.C: This program shows how numbers stored
* as strings can be converted to numeric values
* using the atof, atoi, and atol functions.
*/
#include <stdlib.h>
#include <stdio.h>
void main( void )
{
char *s; double x; int i; long l;
s = " -2309.12E-15"; /* Test of atof */
x = atof( s );
printf( "atof test: ASCII string: %s\tfloat: %e\n", s, x );
s = "7.8912654773d210"; /* Test of atof */
x = atof( s );
printf( "atof test: ASCII string: %s\tfloat: %e\n", s, x );
s = " -9885 pigs"; /* Test of atoi */
i = atoi( s );
printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );
s = "98854 dollars"; /* Test of atol */
l = atol( s );
printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l );
}
Output
atof test: ASCII string: -2309.12E-15 float: -2.309120e-012
atof test: ASCII string: 7.8912654773d210 float: 7.891265e+210
atoi test: ASCII string: -9885 pigs integer: -9885
atol test: ASCII string: 98854 dollars long: 98854
Dr Abudawood
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Hi,
I want to add a window to my application that will show a list of items.
For that I create a CFrameWand with a ClistCtrl view inside.
the problem is that the cunstructor of CFrameWnd is protected by default.
How can I pop up the window ?
Is there a method to do it without touching the specific constructor ?
Shay
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I assume you are talking about a CFrameWnd derrived class of your own created by the class wizzard. You can either use dynamic creation (IMPLEMENT_DYANMIC ...) or make the constructor public yourself. I do the second all the time but in the past I have done some work with creating class instances using the GetRuntimeClass() stuff..
John
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Yes, you are right, I amderiving my own class.
How do I use the "dynamic creation" ?
Or how do I use the GetRunTimeClass() ?
Thanks
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How do I use the "dynamic creation" ?
Look in the documentation for CObject:
CRuntimeClass* pRuntimeClass = RUNTIME_CLASS( CMyClass );
CObject* pObject = pRuntimeClass->CreateObject();
ASSERT( pObject->IsKindOf( RUNTIME_CLASS( CMyClass ) ) );
However it is far easier to just make your constructor public...
John
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Thank you,
I did converted it into public, but I said to myself it was fishy and not menat to be this way...
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It is protected because MFC internals create it using the dynamic method and in most cases the user does not need to do this themselves.
John
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You could use RTTI if you do not want to use MFC.
RUNTIME_CLASS is a macro written by Ms.
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:(I want to find the relation between a font and the Unicode,
I want to know a font’s character set like to http://www.unicode.org/charts/, but I don’t’ know how I can find the character set like it?
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If you're using Windows 2000 or XP, use the Character Map tool (typically in your start menu at Accessories > System Tools > Character Map). Check the Advanced View box.
This won't show you the code points which have no glyph (character image) assigned, but it will show you all the (basic) glyphs that are available in the font, and the code points to which they are assigned.
See here for a guide to Unicode terminology[^], including definitions of glyph, encoding and code point.
--
Mike Dimmick
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I want to find a function that it can know which character can be displayed?
Different font have different character set, for example the font of Arial maybe have five character set and the font of PMingLiU maybe have ten character set. How I can know the number and name of a font’s character set?
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