strncpy, strncpy_s

#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
int main(void)
{
    char src[] = "hi";
    char dest[6] = "abcdef"; // 无空终止符
    strncpy(dest, src, 5); // 向dest写入五个字符 'h', 'i', '\0', '\0', '\0'
    printf("strncpy(dest, src, 5) to a 6-byte dest gives : ");
    for (size_t n = 0; n < sizeof dest; ++n) {
        char c = dest[n];
        c ? printf("'%c' ", c) : printf("'\\0' ");
    }
    printf("\nstrncpy(dest2, src, 2) to a 2-byte dst gives : ");
    char dest2[2];
    strncpy(dest2, src, 2); // 截断：向dest2写入两个字符 'h', 'i'
    for (size_t n = 0; n < sizeof dest2; ++n) {
        char c = dest2[n];
        c ? printf("'%c' ", c) : printf("'\\0' ");
    }
    printf("\n");
#ifdef __STDC_LIB_EXT1__
    set_constraint_handler_s(ignore_handler_s);
    char dst1[6], src1[100] = "hello";
    errno_t r1 = strncpy_s(dst1, 6, src1, 100);  // 向r1写入0，向dst1写入6个字符
    printf("dst1 = \"%s\", r1 = %d\n", dst1,r1); // 向dst1写入 'h','e','l','l','o','\0'
    char dst2[5], src2[7] = {'g','o','o','d','b','y','e'};
    errno_t r2 = strncpy_s(dst2, 5, src2, 7);    // 复制操作溢出目标数组
    printf("dst2 = \"%s\", r2 = %d\n", dst2,r2); // 向r2写入非零值，向dst2[0]写入'\0'
    char dst3[5];
    errno_t r3 = strncpy_s(dst3, 5, src2, 4);    // 向r3写入0，向dst3写入5个字符
    printf("dst3 = \"%s\", r3 = %d\n", dst3,r3); // 向dst3写入 'g', 'o', 'o', 'd', '\0'
#endif
}