C++ keyword: asm - cppreference.com (original) (raw)

[edit] Usage

• Declaration of an inline assembly block

[edit] Example

Note that while this example works well with GCC/Clang on x86_64 platform under Linux, it's not guaranteed elsewhere as asm declaration is conditionally-supported and(since C++11) implementation defined.

#include   int main() noexcept { const char* const c_string = "Hello, world!\n"; asm (R"( movq $1, %%rax # syscall number for sys_write movq $1, %%rdi # file descriptor 1 (stdout) movq %0, %%rsi # pointer to the c‐string movq %1, %%rdx # length of the c‐string syscall # invokes an OS system-call handler )" : // no output operands : "r"(c_string), // input: pointer to the c‐string "r"(std::strlen(c_string)) // input: size of the c‐string : "%rax", "%rdi", "%rsi", "%rdx" // clobbered registers ); }

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