Expanding the Capabilities of SendInput to Transmit Multiple Characters

The SendInput function is a powerful tool in the arsenal of programmers, enabling the simulation of keyboard input. However, its capacity is not limited to transmitting single characters. This article explores how to leverage SendInput to transmit multiple characters effectively.

Initially, one might attempt to use a technique similar to the following:

INPUT in;
in.type = INPUT_KEYBOARD;
in.ki.wScan = 0;
in.ki.time = 0;
in.ki.dwExtraInfo = 0;
in.ki.wVk = 0x53   0x54;

SendInput(2, &in, sizeof(INPUT));

Unfortunately, this code will fail to execute as intended. The reason lies in the first parameter of SendInput, which specifies the number of INPUT structures passed in. In this case, only one structure is provided, contrary to the value of 2 passed to SendInput.

Moreover, it is not possible to use a single INPUT structure to specify multiple virtual keys. To achieve this objective, an array of INPUT structures must be declared, with each pair representing a keydown and keyup event. Thus, for the aforementioned example, four INPUT structures are required.

Another consideration relates to the KEYEVENTF_UNICODE flag. When using this flag, actual Unicode codepoints are specified instead of virtual keys. Each codepoint corresponds to a UTF-16 codeunit, meaning that if a Unicode codepoint requires a surrogate pair, two sets of down/up INPUT structures will be necessary.

To conclude, the correct approach involves declaring an array of INPUT structures, ensuring that the number of structures matches the number of characters to be transmitted. Additionally, if KEYEVENTF_UNICODE is employed, the Unicode codepoints should be correctly handled and the corresponding down/up events specified. By adhering to these guidelines, developers can harness the full potential of SendInput to transmit multiple characters with ease and efficiency.