proc _testp
buffer rb 10
enter
cinvoke wsprintf,buffer,'%s',"Hello"
return
endp
    

proc _testp
buffer rb 10
enter
lea eax,[buffer]
cinvoke wsprintf,eax,'%s',"Hello"
return
endp    

proc _testp
buffer rb 10
enter
cinvoke wsprintf,[buffer],'%s',"Hello" ;Does the trick 
return
endp
    

Oh and another question: I know that I can translate integers into strings with wsprintf (via %d string). Is there also a possibility to translate floating point values into strings? In C, there was this nice "%f" format string, if I remember right.

sprintf proc C ptrBuffer:DWORD, szFormat:DWORD, ptrArguments:VARARG
- description
This is the greatest proc from this library. It formats strings like the wsprintf API, but it is much more powerful. You have the whole control over formatting. See possible formats below:
%% - saves one '%' character
%d - decimal signed number
%u - decimal unsigned number
%x - hexadecimal unsigned number in lowercase
%X - hexadecimal unsigned number in uppercase
%o - octal unsigned number
%b - binary unsigned number
These were just common formats, but check these below:

BASE64:
%@[len] - saves as result base64 string made from given argument of given lenght in '[]' brackets. These are optional, but if you don't put them proc will assume you have pushed string, so it'll count strlen from it. See examples:
%@ - creates base64 from zero-terminated string
%@[100] - creates base64 from some 100 byte long memory

FLOATING POINT:
ATTENTION: It saves 3 digits after the coma ('.' character')
%fd - floating point decimal signed number
%fu - floating point decimal unsigned number
%fx - floating point hexadecimal unsigned number in lowercase
%fX - floating point hexadecimal unsigned number in uppercase
%fo - floating point octal unsigned number
%fb - floating point binary unsigned number

USER_DEFINED:
%padding/precision[base](sign)+
Yes yes yes. You can define your own formats using this template. First of all put in format string '%' character. After it you can put the 'f' character. If so it treats the number as floating point. After you may put '0x' where x is the number 0-9. If this is floating point number this value indicates number of digits after coma ('.' character). If the number is an integer this value is padding amount, for example '08' will pad the result to eight digits. After it You may put '[xx]' string. Put number in bracket that will be the results base. For example '[2]' for binary, '[10]' for decimal. But it may be only value between 2-16 if more it's truncated. After it you can put '(-)' string to indicate that the number is signed. You can also put only '()' if it's unsigned, but if no '(' character is found sprintf assumes the value as unsigned so it's not needed. At last you can put '+' character to indicate that result shoul be in lowercase, but it applies only to numbers of 11-16 base, because only there alphabetical digits exists. You don't have to put all these things in your-defined format. sprintf will default it to the unsigned decimnal integer. I'll show you some examples to study and understand :
%08[10](-) - pad to 8 digits, decimal, signed
%f[16] - hexadecimal, floatinf point, unsigned, 3 digits after coma (I forgot to say that func defaults number of digits after coma to 3)
%04f[12]+ - 4 digits after coma, base 12, lowercase, floating point

ATTENTION: ALL USER-DEFINED FORMATS MUST END WITH SPACE (' ' CHARACTER)
I hope you have understood it, if no feel free to ask me: rev15@wp.pl

- input
ptrBuffer - some place in memory where to save result
szFormat - string containing formats
ptrArguments - variable length array of arguments

- output
eax: bytes written

include 'include/win32ax.inc'

.code
start:
call _main
invoke ExitProcess,0


proc _main
_ptr1 dd ?
enter
cinvoke wsprintf,buffer,'%s',"Hello!"   ;buffer="Hello"
lea eax,[buffer]
mov [_ptr1],dword eax                     ;_ptr1=&buffer;
pushd 0
cinvoke wsprintf,_str1,'%s',"Caption" 
pushd _str1
lea eax,[_ptr1]
cinvoke wsprintf,_str0,'%s',eax          ;_str0=*_ptr1;
pushd _str0
pushd 0
call [MsgBox]
return
endp

.data
buffer rb 20
_str0 rb 21
_str1 rb 6

section '.idata' import data readable writeable
library user32,'user32.dll',\ 
   kernel32,'kernel32.dll'

import user32,\ 
   MsgBox,'MessageBoxA',\ 
   wsprintf,'wsprintfA'

import kernel32,\ 
   ExitProcess,'ExitProcess'

    

Code:

lea eax,[_ptr1]
cinvoke wsprintf,_str0,'%s',eax          ;_str0=*_ptr1;