虽然通过练习3-5中的在C编程语言,我遇到了以下意外行为。为什么变量在C程序中被突变?
#include <stdio.h>
#include <string.h>
// inspired by: http://www.eng.uerj.br/~fariasol/disciplinas/LABPROG/C_language/Kernighan_and_Ritchie/solved-exercises/solved-exercises.html/krx305.html
void reverse(char s[]) {
int c, i, j;
for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
c = s[i];
s[i] = s[j];
s[j] = c;
}
}
void itob(int n, char s[], int b) {
static char digits[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int i = 0,
sign;
if (b < 2 || b > 36) {
fprintf(stderr, "EX3_5: Cannot support base %d\n", b);
}
if ((sign = n) < 0) {
n = -n;
}
do {
s[i++] = digits[n % b];
} while (n /= b);
if (sign < 0) {
s[i++] = '-';
}
s[i] = '\0';
reverse(s);
}
int main() {
int base = 2,
input;
char buffer[5] = "0000";
input = 127;
itob(input, buffer, base);
printf("%d in base %d is %s\n", input, base, buffer);
// 127 in base 2 is 1111111
input = 128;
itob(input, buffer, base);
printf("%d in base %d is %s\n", input, base, buffer);
// 0 in base 2 is 10000000
// Why is input now 0?!
return 0;
}
为什么input
变量存在的值改变(只有当input
大于127
更大)?我是C新手,但这似乎很意外。据我所知,函数参数是按值传递的。
较大'buffer'不够大。你有一个缓冲区溢出和未定义的行为。 – user2357112
将数组函数参数调整为指针参数。虽然指针是按值传递的,但它们可以用来访问调用者的内存。 –
@ user2357112谢谢 - 就是这样。如果您将评论添加为答案,我很乐意接受。 – pdoherty926