【C語言學習筆記】字串拼接的3種方法

昨天晚上和@buptpatriot討論函數返回指標（malloc產生的）的問題，提到字串拼接，做個總結。

#include<stdio.h>#include<stdlib.h>#include<string.h>char *join1(char *, char*);void join2(char *, char *);char *join3(char *, char*);int main(void) {char a[4] = "abc"; // char *a = "abc"char b[4] = "def"; // char *b = "def"char *c = join3(a, b);printf("Concatenated String is %s\n", c);free(c);c = NULL;return 0;}/*方法一，不改變字串a,b, 通過malloc，產生第三個字串c, 返回局部指標變數*/char *join1(char *a, char *b) {char *c = (char *) malloc(strlen(a) + strlen(b) + 1); //局部變數，用malloc申請記憶體if (c == NULL) exit (1);char *tempc = c; //把首地址存下來while (*a != '\0') {*c++ = *a++;}while ((*c++ = *b++) != '\0') {;}//注意，此時指標c已經指向拼接之後的字串的結尾'\0' !return tempc;//傳回值是局部malloc申請的指標變數，需在函數調用結束後free之}/*方法二，直接改掉字串a, 此方法有誤，見留言板*/void join2(char *a, char *b) {//注意，如果在main函數裡a,b定義的是字串常量（如下）：//char *a = "abc";//char *b = "def";//那麼join2是行不通的。//必須這樣定義：//char a[4] = "abc";//char b[4] = "def";while (*a != '\0') {a++;}while ((*a++ = *b++) != '\0') {;}}/*方法三，調用C庫函數,*/char* join3(char *s1, char *s2){    char *result = malloc(strlen(s1)+strlen(s2)+1);//+1 for the zero-terminator    //in real code you would check for errors in malloc hereif (result == NULL) exit (1);    strcpy(result, s1);    strcat(result, s2);    return result;}

參考： http://stackoverflow.com/questions/8465006/how-to-concatenate-2-strings-in-c

           http://www.cplusplus.com/reference/cstdlib/malloc/

           http://www.programmingspark.com/2012/02/c-program-to-concatenate-two-strings.html

update

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留言中，@napoleon_1815 同學說的很對，我的join2方法是不對的，謝謝同學指正。