【C语言学习笔记】字符串拼接的3种方法

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昨天晚上和@buptpatriot讨论函数返回指针（malloc生成的）的问题，提到字符串拼接，做个总结。

#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，不改变字符串a,b, 通过malloc，生成第三个字符串c, 返回局部指针变量*/char *join1(char *a, char *b) {char *c = (char *) malloc(strlen(a) + strlen(b) + 1); //局部变量，用malloc申请内存if (c == NULL) exit (1);char *tempc = c; //把首地址存下来while (*a != '\0') {*c++ = *a++;}while ((*c++ = *b++) != '\0') {;}//注意，此时指针c已经指向拼接之后的字符串的结尾'\0' !return tempc;//返回值是局部malloc申请的指针变量，需在函数调用结束后free之}/*方法二，直接改掉字符串a, 此方法有误，见留言板*/void join2(char *a, char *b) {//注意，如果在main函数里a,b定义的是字符串常量（如下）：//char *a = "abc";//char *b = "def";//那么join2是行不通的。//必须这样定义：//char a[4] = "abc";//char b[4] = "def";while (*a != '\0') {a++;}while ((*a++ = *b++) != '\0') {;}}/*方法三，调用C库函数,*/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;}

参考：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 同学说的很对，我的join2方法是不对的，谢谢同学指正！

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