C++ char 插入字符

// ConsoleApplication6.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//
#include <iostream>
char * insertLast(char *strA, char *strB, char strC)//strA用户数据，strB返回数据, strC插入字符
{
	int m = 0;
	if (strA == NULL)
		return NULL;
	int n = strlen(strA);
	for (int i=0; i<n; i++)
	{
		strB[m]=strA[i];
		m++;
	}
	strB[m++] = strC;
	strB[m++] = '\0';
	return strB;
}

char* insertFirst(char* strA, char* strB, char strC)//strA用户数据，strB返回数据, strC插入字符
{
	int m = 0;
	if (strA == NULL)
		return NULL;
	int n = strlen(strA);
	for (int i = 0; i <=n; i++)
	{
		if (i==0)
			strB[m] = strC;
		else
			strB[m] = strA[i-1];
		m++;
	}
	strB[m] = '\0';
	return strB;
}
int main()
{
	
	{
		char p2[15];
		char p[] = "全部成交";
		int k = strlen(p);
		char* buff = (char*)malloc(k * 2 + 1);
		char* p1 = insertFirst(p, buff, 'A');
		strcpy(p2, p1);
		printf("insertFirst：%s\n", p1);
		free(buff);

	}
	
	{
		char p2[15];
		char p[] = "全部成交";
		int k = strlen(p);
		char* buff = (char*)malloc(k * 2 + 1);
		char* p1 = insertLast(p, buff, 'A');
		strcpy(p2, p1);
		printf("insertLast：%s\n", p2);
		free(buff);
	}
}