* strings.join
// Join concatenates the elements of a to create a single string. The separator string
// sep is placed between elements in the resulting string.
func Join(a []string, sep string) string {
switch len(a) {
case 0:
return ""
case 1:
return a[0]
case 2:
// Special case for common small values.
// Remove if golang.org/issue/6714 is fixed
return a[0] + sep + a[1]
case 3:
// Special case for common small values.
// Remove if golang.org/issue/6714 is fixed
return a[0] + sep + a[1] + sep + a[2]
}
n := len(sep) * (len(a) - 1)
for i := 0; i < len(a); i++ {
n += len(a[i])
}
b := make([]byte, n)
bp := copy(b, a[0])
for _, s := range a[1:] {
bp += copy(b[bp:], sep)
bp += copy(b[bp:], s)
}
return string(b)
}* join.c
#include <stdio.h>
#include <stdlib.h>
size_t len(char *s) {
char *p = s;
size_t len = 0;
while (*p++ != '\0') {
++len;
}
return len;
}
size_t ncopy(char *dst, char *src, size_t n) {
int i = 0;
while (n-- && (*dst++ = *src++)) { i++; }
return i;
}
char *join(char **s, size_t l, char *sep) {
char *r = (char *)0;
int n = 0, i, j;
switch (l) {
case 0:
r = (char *)malloc(sizeof(char));
r[0] = '\0';
return r;
case 1:
n = len(s[0]) * sizeof(char) + 1;
r = (char *)malloc( n );
ncopy(r, s[0], n);
return r;
}
n = len(sep) * (l-1);
for (i = 0; i < l; i++) {
n += len(s[i]);
}
r = (char *)malloc(sizeof(char)*n + 1);
ncopy(r, s[0], len(s[0]));
int f = 0, h = len(sep);
for (i = 1, j = len(s[0]); i < l; i++) {
/* copy separator */
ncopy(&r[j], sep, h);
j += h;
/* copy array elememts */
f = len(s[i]);
ncopy(&r[j], s[i], f);
j += f;
}
r[n*sizeof(char)] = '\0';
return r;
}
int main(int argc, char **argv) {
printf("%lu\n", len("Hello, world!"));
char *a[3] = {"He", "ll", "o"};
char *s = join(a, sizeof(a)/sizeof(a[0]), "::");
printf("%s\n", s);
free(s);
char *b[1] = {"world"};
printf("%s\n", (s = join(b, 1, ",")));
free(s);
char *c[5] = {"a", "b", "c", "d", "e"};
printf("%s\n", (s = join(c, 5, ",")));
free(s);
char *d[4] = {"12","345", "6", "789"};
printf("%s\n", (s = join(d, 4, "")));
free(s);
return 0;
}
* compile
gcc join.c -Wall
* run
./a.out
13
He::ll::o
world
a,b,c,d,e
123456789
