How shell parameters are parsed?

I used this simple script,named echo_arg in a msys shell

echo $1
echo $2
echo $3


For these 2 cases, called from CLI,

$ C:/msys/1.0/bin/sh.exe -c "C:/msys/1.0/bin/sh.exe echo_arg a "b" c"

$ C:/msys/1.0/bin/sh.exe -c "C:/msys/1.0/bin/sh.exe echo_arg a "b" c"

the output was

a
b
c


But CreateProcess function in a C program did not give the same result (compilation with mingw-w64, thread : win32, exception : seh, version : 7.3.0 )

#include <windows.h>
#include <stdio.h>

void main( int argc, char *argv )

int i;
STARTUPINFO si;
PROCESS_INFORMATION pi;

ZeroMemory( &si, sizeof(si) );
si.cb = sizeof(si);
ZeroMemory( &pi, sizeof(pi) );

char * cmd =
"C:/msys/1.0/bin/sh.exe -c "C:/msys/1.0/bin/sh.exe echo_arg a "b" c"",
"C:/msys/1.0/bin/sh.exe -c "C:/msys/1.0/bin/sh.exe echo_arg a \"b\" c"",
"C:/msys/1.0/bin/sh.exe -c "/bin/sh.exe echo_arg a \"b\" c"" ;

for (i=0;i<3;i++)
printf("t%sn",cmd[i]);
CreateProcess(NULL, cmd[i] , NULL,NULL,FALSE,0,NULL,NULL,&si,&pi);
WaitForSingleObject( pi.hProcess, INFINITE );
CloseHandle( pi.hProcess );
CloseHandle( pi.hThread );




Ouput :

C:/msys/1.0/bin/sh.exe -c "C:/msys/1.0/bin/sh.exe echo_arg a "b" c"
a
b
c

C:/msys/1.0/bin/sh.exe -c "C:/msys/1.0/bin/sh.exe echo_arg a "b" c"
a
b c

C:/msys/1.0/bin/sh.exe -c "/bin/sh.exe echo_arg a "b" c"
a
b
c

Why, in the second case, b and c are not separated ($2="b c" and $3 is empty) ? And why case 3 worked.

Only for information, I am not a mad man that likes to play with " " / ... I have encountered this problem when I was trying to install GNU MP library (OS : windows 10). It did not work and it was the beginning of a long story before I found the cause.

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