how to write assembly language programs in c++? what is use of asm ?

Assembly language appears in two flavors: Intel Style & AT&T style. GNU C compiler i.e. GCC uses AT&T syntax and this is what we would use. Let us look at some of the major differences of this style as against the Intel Style. Register Naming: Register names are prefixed with %, so that registers are %eax, %cl etc, instead of just eax, cl. Ordering of operands: Unlike Intel convention (first operand is destination), the order of operands is source(s) first, and destination last. For example, Intel syntax "mov eax, edx" will look like "mov %edx, %eax" in AT&T assembly. Operand Size: In AT&T syntax, the size of memory operands is determined from the last character of the op-code name. The suffix is b for (8-bit) byte, w for (16-bit) word, and l for (32-bit) long. For example, the correct syntax for the above instruction would have been "movl %edx, %eax". Immediate Operand: Immediate operands are marked with a $ prefix, as in "addl $5, %eax", which means add immediate long value 5 to register %eax). Memory Operands: Missing operand prefix indicates it is a memory-address; hence "movl $bar, %ebx" puts the address of variable bar into register %ebx, but "movl bar, %ebx" puts the contents of variable bar into register %ebx. Indexing: Indexing or indirection is done by enclosing the index register or indirection memory cell address in parentheses. For example, "movl 8(%ebp), %eax" (moves the contents at offset 8 from the cell pointed to by %ebp into register %eax). read less

Generally the inline term is used to instruct the compiler to insert the code of a function into the code of its caller at the point where the actual call is made. Such functions are called "inline functions". The benefit of inlining is that it reduces function-call overhead. Now, it's easier to guess about inline assembly. It is just a set of assembly instructions written as inline functions. Inline assembly is used for speed, and you ought to believe me that it is frequently used in system programming. We can mix the assembly statements within C/C++ programs using keyword asm. Inline assembly is important because of its ability to operate and make its output visible on C/C++ variables. Assembly language appears in two flavors: Intel Style & AT&T style. GNU C compiler i.e. GCC uses AT&T syntax and this is what we would use. Let us look at some of the major differences of this style as against the Intel Style. If you are wondering how you can use GCC on Windows, you can just download Cygwin from www.cygwin.com. Register Naming: Register names are prefixed with %, so that registers are %eax, %cl etc, instead of just eax, cl. Ordering of operands: Unlike Intel convention (first operand is destination), the order of operands is source(s) first, and destination last. For example, Intel syntax "mov eax, edx" will look like "mov %edx, %eax" in AT&T assembly. Operand Size: In AT&T syntax, the size of memory operands is determined from the last character of the op-code name. The suffix is b for (8-bit) byte, w for (16-bit) word, and l for (32-bit) long. For example, the correct syntax for the above instruction would have been "movl %edx, %eax". Immediate Operand: Immediate operands are marked with a $ prefix, as in "addl $5, %eax", which means add immediate long value 5 to register %eax). Memory Operands: Missing operand prefix indicates it is a memory-address; hence "movl $bar, %ebx" puts the address of variable bar into register %ebx, but "movl bar, %ebx" puts the contents of variable bar into register %ebx. Indexing: Indexing or indirection is done by enclosing the index register or indirection memory cell address in parentheses. For example, "movl 8(%ebp), %eax" (moves the contents at offset 8 from the cell pointed to by %ebp into register %eax). read less

The __asm keyword invokes the inline assembler and can appear wherever a C or C++ statement is legal. It must be followed by an assembly instruction, a group of instructions enclosed in braces, or, at the very least, an empty pair of braces. The term "__asm block" here refers to any instruction or group of instructions, whether or not in braces. example: __asm { mov al, 2 mov dx, 0xD007 out dx, al } read less

Nice Questions , Assemble language or coding are use to interface with processors , You can say direct command , C or C++ is just another layer who offer user friendly commands who invoke action and transfer asm to machine level language .Asm Language is Processor language who use memory management operation mostly , keywords are like PUSH-POP etc .MAchine just understand "0" and "1" i.e machine level language . *.a(lib) ,*.o(object) are input for Linker , Linker offer -*.lib,*.dll.*.exe,*.out files which is the input for Loader ,Loader relocate Memory For Task. For More Information please click on following links for better understanding.. http://www.bogotobogo.com/cplusplus/assembly.php read less