打印从C函数返回的字符数组 [英] Printing array of characters returned from function in C
问题描述
我是C语言的新手,所以请您谅解初学者的问题.
I'm a newbie in C language, so forgive me the beginners question.
#include<stdio.h>
#include<stdlib.h>
char *decimal_to_binary(int);
void main() {
int buffer;
while (1) {
printf("Type your number here: \n\r");
scanf_s("%d", &buffer);
printf("After conversion to binary system your number is: \n\r");
printf("%s", decimal_to_binary(buffer));
printf("\n");
}
}
int get_byte_value(int num, int n) {
// int x = (num >> (8*n)) & 0xff
return 0;
}
char* decimal_to_binary(int num) {
int tab[sizeof(int) * 8] = { 0 };
char binary[sizeof(int) * 8] = { 0 };
int i = 0;
while (num) {
tab[i] = num % 2;
num /= 2;
i++;
}
for (int j = i - 1, k = 0; j >= 0; j--, k++) {
binary[k] = tab[j];
}
return binary;
}
当我打印出从decimal_to_binary返回的所有内容时,我得到了一些垃圾(笑脸字符)而不是二进制表示形式.但是,当我在 decimal_to_binary
函数的最后一个循环中执行 printf
时,我得到的是正确的值.那我做错了什么?
When I print out whatever came back from decimal_to_binary I get some garbage (a smiley face character) instead of the binary representation. But when I do printf
inside the last loop of the decimal_to_binary
function, I'm getting correct values. So what did I do wrong?
推荐答案
此
char binary[sizeof(int) * 8] = { 0 };
是局部变量声明,您不能返回它.
is a local variable declaration, you can't return that.
您需要使用堆从函数返回数组,为此您需要 malloc()
You need to use the heap to return an array from a function, for that you need malloc()
char *binary; /* 'binary' is a pointer */
/* multiplying sizeof(int) will allocate more than 8 characters */
binary = malloc(1 + 8);
if (binary == NULL)
return NULL;
binary[sizeof(int) * 8] = '\0'; /* you need a '\0' at the end of the array */
/* 'binary' now points to valid memory */
接下来,分配 binary [k] = tab [j];
可能不是您所想的
Next the assignment binary[k] = tab[j];
is probably not what you think
binary[k] = (char)(tab[j] + '0');
可能就是您想要的.
注释:c中的字符串只是带有终止符'\ 0'的字节序列.
note: strings in c are just sequences of bytes with a terminating '\0'.
修复此问题后,您还需要修复 main()
,现在就执行此操作
After fixing this, you need to fix main()
too, doing this now
printf("%s", decimal_to_binary(buffer));
是错误的,因为 decimal_to_binary()
可能返回 NULL
,并且因为您需要在缓冲区返回后释放它,所以
is wrong, because decimal_to_binary()
could return NULL
, and because you need to free the buffer after it's returned, so
char *binstring = decimal_to_binary(buffer);
if (binstring != NULL)
printf("%s", binstring);
free(binstring);
另外,请注意,您只计算 8
位,因此 decimal_to_binary
的适当签名应为
also, notice that you are only computing 8
bits, so an appropriate signature for decimal_to_binary
would be
char *decimal_to_binary(int8_t value);
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