Why push ecx ?

From: sugaray (ruicui_at_sohu.com)
Date: 01/25/04 

Date: Sun, 25 Jan 2004 19:49:51 +0000 (UTC)

Hi, I have a question here, VC7 generated such assembly code for my
strlen()

_strlen PROC NEAR
        push ebp
        mov ebp, esp
        push ecx
        mov eax, DWORD PTR [ebp+8]
        mov DWORD PTR [ebp-4], eax
$L1:
        mov ecx, DWORD PTR [ebp-4]
        movsx edx, BYTE PTR [ecx]
        test edx, edx
        je SHORT $L2
        mov eax, DWORD PTR [ebp-4]
        add eax, 1
        mov DWORD PTR [ebp-4], eax
        jmp SHORT $L1
$L2:
        mov eax, DWORD PTR [ebp-4]
        sub eax, DWORD PTR [ebp+8]
        mov esp, ebp
        pop ebp
        ret 0
_strlen ENDP

the C code of my strlen() is as below

unsigned int strlen(const char *s) {
       const char *t=s;
       while(*t!='\0') ++t;
       return t-s;
}

i don't know why 'push ecx' after the prologue code, ain't edx and eax
in used later in the assembly code, why not push them ? can somebody
point out why for me ? thanx.