Question

经过很长一段时间我在C中玩动态内存分配，我遇到了内存泄漏的一些问题......我只是看不出问题出在哪里。任何人都可以帮忙吗？

EDIT2：程序现在工作正常，即使有非常大的数字，并且很快:)我决定改变程序结构并使用struct而不仅仅是char字符串。不应该有任何内存泄漏（使用valgrind测试）。

当前代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct binary{
    char * number;
    size_t length;
}Tbinary;

//exterminate leading zeros
size_t exterminate(char * bin, size_t length){
char * pch = NULL;
long position = 0;

pch = strchr(bin, '1');
if(pch==NULL){
    bin[1] = '\0';
    length = 2;
}
else{
    position = pch-bin;
    strcpy(bin, pch);
}

return (length-position);
}

int binaryAdd(Tbinary first, Tbinary second){
int a=0, b=0, sum=0, carry=0;
size_t index = first.length;
first.number[first.length] = '\0';

while((first.length != 0) || (carry != 0)){
    if(first.length>1) a= first.number[first.length-2]-'0';
    else a = 0;
    if(second.length>1) b= second.number[second.length-2]-'0';
    else b = 0;
    sum = (a+b+carry)%2;
    first.number[first.length-1] = (sum)+'0';
    carry = (a+b+carry)/2;
    if(first.length >0)first.length--;
    if(second.length >0)second.length--;
}

exterminate(first.number,index);

printf("Sum: %s\n", first.number);
return EXIT_SUCCESS;
}

int get_number(Tbinary *bin_addr){
char * tmp, * bin;
char ch=1;
int size = 1, index = 0;
bin = bin_addr->number;

while(ch){
    ch = getc(stdin);

    if((ch == '\n') || (ch == ' ')) ch = '\0';

    if((ch-'0' != 0) && (ch-'0' != 1) && (ch != '\0')) return EXIT_FAILURE;

    if (size-1 <=index){
        size += 5;
        tmp = (char *)realloc(bin, size*sizeof(char));
        if(tmp == NULL){
            return EXIT_FAILURE;
        }
        bin = tmp;
        bin_addr->number = bin;
    }
    bin[index++] = ch;
}

bin_addr->length = index;
bin_addr->length = exterminate(bin_addr->number, bin_addr->length);

return EXIT_SUCCESS;
} 

int main (void)
{
Tbinary bin1 = {bin1.number = NULL, bin1.length = 0};
Tbinary bin2 = {bin2.number = NULL, bin2.length = 0};

//allocate space for first number
bin1.number = (char *)malloc(sizeof(char));
if(bin1.number == NULL)
    return EXIT_FAILURE;

//allocate space for second number
bin2.number = (char *)malloc(sizeof(char));
if(bin2.number == NULL){
    free(bin1.number);
    return EXIT_FAILURE;
}

printf("Enter two binary numbers:\n");

//number1 load
if(get_number(&bin1) != EXIT_SUCCESS){
    free(bin1.number);
    free(bin2.number);
    printf("Invalid input.\n");
    return EXIT_FAILURE;
}

//number2 load
if(get_number(&bin2) != EXIT_SUCCESS){
    free(bin1.number);
    free(bin2.number);
    printf("Invalid input.\n");
    return EXIT_FAILURE;
}

//add the two numbers
if(bin1.length >= bin2.length){
    if(binaryAdd(bin1, bin2) != EXIT_SUCCESS){
        free(bin1.number);
        free(bin2.number);
        printf("Invalid input.\n");
        return EXIT_FAILURE;
    }
}
else{
    if(binaryAdd(bin2, bin1) != EXIT_SUCCESS){
        free(bin1.number);
        free(bin2.number);
        printf("Invalid input.\n");
        return EXIT_FAILURE;
    }
}

free(bin1.number);
free(bin2.number);
return EXIT_SUCCESS;
}

Answer 1

在binaryAdd（）中，你应该在realloc（）之后在所有情况下释放sum，而不仅仅是当realloc（）返回null时。 get_number（）中的内容相同。关于a = (int)strlen(first);为什么要将strlen（）的返回转换为int？另外，不要强制转换分配函数。

Answer 2

您的size和index关系中出现了一个错误：

    if (size <=index){
        size += 5;
        tmp = (char *)realloc(sum, size*sizeof(char));
        if(tmp == NULL){
            free(sum);  // free memory to avoid leak
            return EXIT_FAILURE;
        }
        sum = tmp;
    }
    for(int i=index; i>0; i--){
        sum[i] = sum[i-1];
    }
    sum[0] = num%2+'0';
    carry = num/2;
    index++;
}
sum[index] = '\0';

如果在进入最后一次迭代index == size-1时，您正在写入已分配的内存之外。有时这可能是无害的，对于其他人，您可能会覆盖一些重要数据而不会立即崩溃，有时它可能导致立即崩溃（当越界访问跨越页面边界时，通常）。将测试更改为size - 1 <= index。

在get_number中，如果需要realloc，则只需将char*的本地副本更改为输入缓冲区，因此如果位置发生更改，则{{1}中的指针指向无效的内存。它应该是

main

并在int get_number(char **bin_addr){ char * tmp, bin = *bin_addr; char ch=1; size_t size = 1, index = 0; while(ch){ ch = getc(stdin); if((ch == '\n') || (ch == ' ')){ ch = '\0'; } if((ch-'0' != 0) && (ch-'0' != 1) && (ch != '\0')){ return EXIT_FAILURE; } if (size-1 <=index){ size += 5; tmp = (char *)realloc(bin, size*sizeof(char)); if(tmp == NULL){ return EXIT_FAILURE; } bin = tmp; *bin_addr = bin; // let the pointer always point to the real block } bin[index++] = ch; } return EXIT_SUCCESS; }中调用get_number(&bin1);。

二进制添加动态内存分配

2 个答案: