我們常常會需要比對字串/指令後, 執行對應的function, 常見的就是用for loop把command table比對過一次, 但是如果command table大, 效率就不好, 可以用qsort()+bsearch()做binary search以提升效率.
#include <stdio.h> #include <string.h> typedef void (*cmd_fp)(char *cmd);
/* * command function */ void hello(char *cmd) { printf("%s(#%d)\n", __FUNCTION__, __LINE__); }
/* * command function */ void world(char *cmd) { printf("%s(#%d)\n", __FUNCTION__, __LINE__); } /* The structure for command entry */ struct cmd_ent { char const * cmd; cmd_fp fp; } /* Command table - a command array */ cmd_tab[] = { {"hello", hello}, {"world", world}, }; #define AR_SZ(a) (sizeof(a)/sizeof(a[0])) int main(int argc, char *argv[]) { char cmd[64]; int i; while(fgets(cmd, sizeof(cmd) - 1, stdin)) { cmd[strlen(cmd) - 1] = 0; for (i = 0; i < AR_SZ(cmd_tab); i++) { if (strcmp(cmd, cmd_tab[i].cmd) == 0) { cmd_tab[i].fp(cmd); break; } } if (i == AR_SZ(cmd_tab)) { printf("cmd not found\n"); } } }
qsort() + bsearch() version
#include <stdio.h> #include <string.h> #include <stdlib.h> typedef void (*cmd_fp)(char *cmd);
/* * command function */ void hello(char *cmd) { printf("%s(#%d)\n", __FUNCTION__, __LINE__); }
/* * command function */ static void world(char *cmd) { printf("%s(#%d)\n", __FUNCTION__, __LINE__); }
/* The structure for command entry */ struct cmd_ent { char const * cmd; cmd_fp fp; };
/* Command table that is qsort() + bsearch() version */ static struct cmd_tab { int sz; // total htab size int count; // how many comand entry stored in htab. struct cmd_ent *htab; } cmd_tab; /* * increas htab. it will be invoked once htab is full. */ static struct cmd_ent * realloc_htab_and_copy(int new_sz, struct cmd_ent *otab, int num) { struct cmd_ent *ntab; ntab = (struct cmd_ent *) malloc(sizeof(struct cmd_ent) * new_sz); memset(ntab, 0, sizeof(struct cmd_ent) * new_sz); if (num) { memcpy(ntab, otab, sizeof(struct cmd_ent) * num); free(otab); } return ntab; } /* compare function is used for qsort()/sorting or bsearch()/searching */ static int compmi(const void *v1, const void *v2) { struct cmd_ent* e1 = (struct cmd_ent*) v1; struct cmd_ent* e2 = (struct cmd_ent*) v2; return strcmp(e1->cmd, e2->cmd); } /* used for registering a new "cmd"/"fp" into comand table */ static void reg_cmd(char *cmd, cmd_fp fp) { if (cmd_tab.sz == cmd_tab.count) { cmd_tab.sz = (cmd_tab.sz + 16) * 2; cmd_tab.htab = realloc_htab_and_copy(cmd_tab.sz, cmd_tab.htab, cmd_tab.count); } cmd_tab.htab[cmd_tab.count].cmd = cmd; cmd_tab.htab[cmd_tab.count].fp = fp; cmd_tab.count++; qsort(cmd_tab.htab, cmd_tab.count, sizeof(struct cmd_ent), compmi); } /* an example to register two commands into command table */ static void reg_cmds(void) { reg_cmd("hello", hello); reg_cmd("world", world); } int main(int argc, char *argv[]) { char cmd[64]; struct cmd_ent key, *res; int i; reg_cmds(); while(fgets(cmd, sizeof(cmd) - 1, stdin)) { /* main body for command searching */ cmd[strlen(cmd) - 1] = 0; key.cmd = cmd; res = bsearch(&key, cmd_tab.htab, cmd_tab.count, sizeof(struct cmd_ent), compmi); if (res == NULL) { printf("cmd not found\n"); } else { res->fp(cmd); } } }
