help using_mktemp with file extension

[rachelason]

HI!
I want to create unique file names using _mktemp with extension.
This is a code i picked up from MSDN. But if i add .doc or any other extension in the temp pointer, it throws an error. I tried using another variable and concatenating with the original name,,, no good.
any suggestion? Thanks

#include <io.h>
#include <string.h>
#include <stdio.h>

char *temp = "fnXXXXXX";
char *result;
char names[5][20];


int main( void )
{
int i;
FILE *fp;

for( i = 0; i < 5; i++ )
{

strcpy( names, temp );
/* Attempt to find a unique filename: */
result = _mktemp( names);
if( result == NULL )
printf( "Problem creating the template" );
else
{
if( (fp = fopen( result, "w" )) != NULL )
printf( "Unique filename is %s\n", result );
else
printf( "Cannot open %s\n", result );
fclose( fp );}


} return 0;
}

 

[Salem]

Please use the [code][/code] tags when posting code.

Temp files are short-lived files which the program itself uses to store temporary data, and they're usually deleted by the time the program exits. If only the program is going to use the file, then it doesn't care about what it is called, just so long as it's unique.

Applying an extension implies a purpose, and implies that the user will see these files persist beyond the end of the program. In which case, you should really be asking the user for a meaningful filename.

I've seen some programs effectively to mktemp() to create the file initially, then follow that with a rename() to rename the file to the actual name the user requested.

--

 

[cpjust]

I don't know exactly what's going on, but my guess is that _mktemp() wasn't designed to take any other characters after the X's. But if you're interested, I traced the assembly down to the spot where it blows up...

Start of _mktemp()

[b]7816433B[/b]  push        esi  
7816433C  mov         esi,dword ptr [esp+8] 
78164340  push        edi  
78164341  xor         edi,edi 
78164343  cmp         esi,edi 
78164345  jne         78164363 
78164347  call        7813434E 
7816434C  push        edi  
7816434D  push        edi  
7816434E  push        edi  
7816434F  push        edi  
78164350  push        edi  
78164351  mov         dword ptr [eax],16h 
78164357  call        781388FC 
7816435C  add         esp,14h 
7816435F  xor         eax,eax 
78164361  jmp         7816437C 
78164363  push        esi  
78164364  call        78144340 
78164369  inc         eax  
7816436A  push        eax  
7816436B  push        esi  
7816436C  call        7816422D 				<-- Boom in here!
78164371  add         esp,0Ch 
78164374  neg         eax  
78164376  sbb         eax,eax 
78164378  not         eax  
7816437A  and         eax,esi 
7816437C  pop         edi  
7816437D  pop         esi  
7816437E  ret              

-----------------------------------------------------

[b]7816422D[/b]  push        ebp  
7816422E  mov         ebp,esp 
78164230  push        ecx  
78164231  push        ebx  
78164232  push        esi  
78164233  push        edi  
78164234  mov         edi,dword ptr [ebp+8] 
78164237  xor         ebx,ebx 
78164239  cmp         edi,ebx 
7816423B  je          78164242 
7816423D  cmp         dword ptr [ebp+0Ch],ebx 
78164240  ja          78164260 
78164242  call        7813434E 
78164247  push        16h  
78164249  pop         esi  
7816424A  push        ebx  
7816424B  push        ebx  
7816424C  push        ebx  
7816424D  push        ebx  
7816424E  push        ebx  
7816424F  mov         dword ptr [eax],esi 
78164251  call        781388FC 				<-- Boom in here!
78164256  add         esp,14h 
78164259  mov         eax,esi 
7816425B  jmp         78164336 
78164260  push        dword ptr [ebp+0Ch] 
78164263  push        edi  
78164264  call        781500DF 
78164269  mov         esi,eax 
7816426B  cmp         esi,dword ptr [ebp+0Ch] 
7816426E  pop         ecx  
7816426F  pop         ecx  
78164270  mov         dword ptr [ebp+8],esi 
78164273  jb          78164279 
78164275  mov         byte ptr [edi],bl 
78164277  jmp         78164242 
78164279  call        78132FCD 
7816427E  mov         dword ptr [ebp-4],eax 
78164281  mov         eax,dword ptr [ebp+8] 
78164284  add         esi,edi 
78164286  cmp         eax,6 
78164289  jb          78164275 
7816428B  cmp         dword ptr [ebp+0Ch],eax 
7816428E  jbe         78164275 
78164290  mov         dword ptr [ebp+8],ebx 
78164293  jmp         781642C2 
78164295  push        esi  
78164296  push        edi  
78164297  call        78166A0D 
7816429C  test        eax,eax 
7816429E  pop         ecx  
7816429F  pop         ecx  
781642A0  jne         781642C7 
781642A2  cmp         byte ptr [esi],58h 
781642A5  jne         78164275 
781642A7  cmp         dword ptr [ebp+8],5 
781642AB  jae         781642C7 
781642AD  mov         eax,dword ptr [ebp-4] 
781642B0  push        0Ah  
781642B2  xor         edx,edx 
781642B4  pop         ecx  
781642B5  div         eax,ecx 
781642B7  inc         dword ptr [ebp+8] 
781642BA  add         dl,30h 
781642BD  mov         byte ptr [esi],dl 
781642BF  mov         dword ptr [ebp-4],eax 
781642C2  dec         esi  
781642C3  cmp         esi,edi 
781642C5  jae         78164295 
781642C7  cmp         byte ptr [esi],58h 
781642CA  jne         78164275 
781642CC  cmp         dword ptr [ebp+8],5 
781642D0  jb          78164275 
781642D2  mov         byte ptr [esi],61h 
781642D5  mov         dword ptr [ebp+8],62h 
781642DC  call        7813434E 
781642E1  mov         eax,dword ptr [eax] 
781642E3  mov         dword ptr [ebp-4],eax 
781642E6  call        7813434E 
781642EB  push        ebx  
781642EC  push        edi  
781642ED  mov         dword ptr [eax],ebx 
781642EF  call        7815471C 
781642F4  test        eax,eax 
781642F6  pop         ecx  
781642F7  pop         ecx  
781642F8  je          78164304 
781642FA  call        7813434E 
781642FF  cmp         dword ptr [eax],0Dh 
78164302  jne         78164314 
78164304  cmp         dword ptr [ebp+8],7Bh 
78164308  je          78164322 
7816430A  mov         al,byte ptr [ebp+8] 
7816430D  inc         dword ptr [ebp+8] 
78164310  mov         byte ptr [esi],al 
78164312  jmp         781642E6 
78164314  call        7813434E 
78164319  mov         ecx,dword ptr [ebp-4] 
7816431C  mov         dword ptr [eax],ecx 
7816431E  xor         eax,eax 
78164320  jmp         78164336 
78164322  mov         byte ptr [edi],bl 
78164324  call        7813434E 
78164329  mov         dword ptr [eax],11h 
7816432F  call        7813434E 
78164334  mov         eax,dword ptr [eax] 
78164336  pop         edi  
78164337  pop         esi  
78164338  pop         ebx  
78164339  leave            
7816433A  ret              
7816433B  push        esi  
7816433C  mov         esi,dword ptr [esp+8] 
78164340  push        edi  
78164341  xor         edi,edi 
78164343  cmp         esi,edi 
78164345  jne         78164363 
78164347  call        7813434E 
7816434C  push        edi  
7816434D  push        edi  
7816434E  push        edi  
7816434F  push        edi  
78164350  push        edi  
78164351  mov         dword ptr [eax],16h 
78164357  call        781388FC 
7816435C  add         esp,14h 
7816435F  xor         eax,eax 
78164361  jmp         7816437C 
78164363  push        esi  
78164364  call        78144340 
78164369  inc         eax  
7816436A  push        eax  
7816436B  push        esi  
7816436C  call        7816422D 
78164371  add         esp,0Ch 
78164374  neg         eax  
78164376  sbb         eax,eax 
78164378  not         eax  
7816437A  and         eax,esi 
7816437C  pop         edi  
7816437D  pop         esi  
7816437E  ret              

-----------------------------------------------------

[b]781388FC[/b]  push        ebp  
781388FD  mov         ebp,esp 
781388FF  push        dword ptr ds:[781C4028h] 
78138905  call        78132BD7 
7813890A  test        eax,eax 
7813890C  pop         ecx  
7813890D  je          78138912 
7813890F  pop         ebp  
78138910  jmp         eax  
78138912  push        2    
78138914  call        7813BBF2
78138919  pop         ecx  
7813891A  pop         ebp  
7813891B  jmp         781387D1 				<-- Jump & boom in here
78138920  xor         eax,eax 
78138922  push        eax  
78138923  push        eax  
78138924  push        eax  
78138925  push        eax  
78138926  push        eax  
78138927  call        781388FC 
7813892C  add         esp,14h 
7813892F  ret              

-----------------------------------------------------

[b]781387D1[/b]  push        ebp  
781387D2  lea         ebp,[esp-2A8h] 
781387D9  sub         esp,328h 
781387DF  mov         eax,dword ptr ds:[781C19C8h] 
781387E4  xor         eax,ebp 
781387E6  mov         dword ptr [ebp+2A4h],eax 
781387EC  push        esi  
781387ED  mov         dword ptr [ebp+88h],eax 
781387F3  mov         dword ptr [ebp+84h],ecx 
781387F9  mov         dword ptr [ebp+80h],edx 
781387FF  mov         dword ptr [ebp+7Ch],ebx 
78138802  mov         dword ptr [ebp+78h],esi 
78138805  mov         dword ptr [ebp+74h],edi 
78138808  mov         word ptr [ebp+0A0h],ss 
7813880F  mov         word ptr [ebp+94h],cs 
78138816  mov         word ptr [ebp+70h],ds 
7813881A  mov         word ptr [ebp+6Ch],es 
7813881E  mov         word ptr [ebp+68h],fs 
78138822  mov         word ptr [ebp+64h],gs 
78138826  pushfd           
78138827  pop         dword ptr [ebp+98h] 
7813882D  mov         esi,dword ptr [ebp+2ACh] 
78138833  lea         eax,[ebp+2ACh] 
78138839  mov         dword ptr [ebp+9Ch],eax 
7813883F  mov         dword ptr [ebp-28h],10001h 
78138846  mov         dword ptr [ebp+90h],esi 
7813884C  mov         eax,dword ptr [eax-4] 
7813884F  push        50h  
78138851  mov         dword ptr [ebp+8Ch],eax 
78138857  lea         eax,[ebp-80h] 
7813885A  push        0    
7813885C  push        eax  
7813885D  call        78144890 
78138862  lea         eax,[ebp-80h] 
78138865  mov         dword ptr [ebp-30h],eax 
78138868  lea         eax,[ebp-28h] 
7813886B  add         esp,0Ch 
7813886E  mov         dword ptr [ebp-80h],0C000000Dh 
78138875  mov         dword ptr [ebp-74h],esi 
78138878  mov         dword ptr [ebp-2Ch],eax 
7813887B  call        dword ptr ds:[781940F0h] 
78138881  push        0    
78138883  mov         esi,eax 
78138885  call        dword ptr ds:[781940ECh] 
7813888B  lea         eax,[ebp-30h] 
7813888E  push        eax  
7813888F  call        dword ptr ds:[781940E8h] 
78138895  test        eax,eax 
78138897  jne         781388A5 
78138899  test        esi,esi 
7813889B  jne         781388A5 
7813889D  push        2    
7813889F  call        7813BBF2 
781388A4  pop         ecx  
781388A5  push        0C000000Dh 
781388AA  call        dword ptr ds:[781940E4h] 
781388B0  push        eax  
781388B1  call        dword ptr ds:[781940E0h] 		<-- Boom in here!
781388B7  mov         ecx,dword ptr [ebp+2A4h] 
781388BD  xor         ecx,ebp 
781388BF  pop         esi  
781388C0  call        781398EF 
781388C5  add         ebp,2A8h 
781388CB  leave            
781388CC  ret              

-----------------------------------------------------

[b]7C801E16[/b]  mov         edi,edi 
7C801E18  push        ebp  
7C801E19  mov         ebp,esp 
7C801E1B  cmp         dword ptr [ebp+8],0 
7C801E1F  jne         7C801E2A 
7C801E21  push        6    
7C801E23  call        7C8092B0 
7C801E28  jmp         7C801E45 
7C801E2A  push        dword ptr [ebp+0Ch] 
7C801E2D  push        dword ptr [ebp+8] 
7C801E30  call        dword ptr ds:[7C8013FCh] 		<-- Boom in here!
7C801E36  test        eax,eax 
7C801E38  jl          7C801E3F 
7C801E3A  xor         eax,eax 
7C801E3C  inc         eax  
7C801E3D  jmp         7C801E47 
7C801E3F  push        eax  
7C801E40  call        7C80936B 
7C801E45  xor         eax,eax 
7C801E47  pop         ebp  
7C801E48  ret         8    

-----------------------------------------------------

[b]7C90E88E[/b]  mov         eax,101h 
7C90E893  mov         edx,7FFE0300h 
7C90E898  call        dword ptr [edx] 			<-- Boom in here!
7C90E89A  ret         8    

-----------------------------------------------------

[b]7C90EB8B[/b]  mov         edx,esp 
7C90EB8D  sysenter         				<-- Boom in here!
7C90EB8F  nop              
7C90EB90  nop              
7C90EB91  nop              
7C90EB92  nop              
7C90EB93  nop              
7C90EB94  ret              


State of registers before entering "sysenter":

EAX = 00000101 EBX = 00000000 ECX = 7C8637FA EDX = 0012FBD4 ESI = 00000001 
EDI = 00403380 EIP = 7C90EB8D ESP = 0012FBD4 EBP = 0012FBE4 EFL = 00000286

 

[rachelason]

HI everyone,
thanks for the reply.
I am not keen on using just _mktemp. All i want to be able to do is create a unique filename(.xml is what i am trying to create) and if the user saves it , i would let the program save it for the user or delete the object.

I tried creating a unique file name and then rename it(just adding extension) but _mktemp does not recognise the existing one as it does not count files with extension.
Yes, _mktemp does not allow any extension. Is there any other function i can use to create unique file name.

Also, can anyone tell me is there any book on c++ which gives information about standard libriries and all the attached methods and variable? Say if i want the same in Java, Deital and Deital , which not only teaches how to program but also explains all the methods of standard library.
Thanks

 

[cpjust]

OK first, if you create a temp file and the user doesn't want to save it, you don't need any extension since it's going to be deleted anyways.
Now, if the user does want to save it, I'm pretty sure they don't want to use the filename created by mktemp(). So you should ask them what name to use. Then check if that file exists; if it does, ask if they want to overwrite it...