c语言子函数返回字符串的错误
最近做leetcode上的一道题,通过子函数返回字符串。开始时用局部变量的字符串返回的,认为返回了字符串的首地址,便可以get到这个字符串,但由于局部变量离开函数后被回收了,因此字符串首地址是收到了,但是所在内容却被回收,因此出错。
//这是出错代码
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char* intToRoman(int num) {
int base[13] = { 1000,900,500,400,100,90,50,40,10,9,5,4,1 };
char * basestr[13] = { "M","CM","D","DM","C","XC","L","XL","X","IX","V","IV","I" };
int count[13];
for (int i = 0; i < 13; i++) {
count[i] = num / base[i];
num -= base[i] * count[i];
}
char s[100];//这样子是局部变量
int index = 0;
for (int i = 0; i < 13; i++) {
for (int j = 0; j < count[i]; j++) {
strcpy(s + index, basestr[i]);
index += strlen(basestr[i]);
}
}
s[index] = '\0';
return s;
}
int main() {
printf("%s",intToRoman(3));
}
正确做法
法一:通过malloc函数分配
因为malloc函数分配内存在堆区,运行过程中由程序员自己管理,系统不回收。
char* intToRoman(int num) {
int base[13] = { 1000,900,500,400,100,90,50,40,10,9,5,4,1 };
char * basestr[13] = { "M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I" };
int count[13];
for (int i = 0; i < 13; i++) {
count[i] = num / base[i];
num -= base[i] * count[i];
}
char *s=(char*)malloc(sizeof(char)*100);
int index = 0;
for (int i = 0; i < 13; i++) {
for (int j = 0; j < count[i]; j++) {
strcpy(s + index, basestr[i]);
index += strlen(basestr[i]);
}
}
s[index] = '\0';
return s;
}
法二:
通过引用传递(或者说传指针)
法三:
全局变量(不推荐)