C 内存错误

标签 c valgrind calloc

我必须采用字符串表示的数字并对它们执行加法运算。这是为了家庭作业，到目前为止我所做的还算有效。它输出正确的输出，但我的程序还需要没有内存错误，但事实并非如此。

有人可以提供有关这些未初始化变量的情况的任何帮助都会很有帮助。我以为是用了malloc而不是calloc，但是我也改了，还是没有骰子。

这是我的输出:

./a.out
strlen: 12
Old: 12122334455
New: 012122334455
Result: 167244668910

这是我的代码: /* * 文件:strmath.c */

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

int cmp(char *, char *, int);
void add(char *, char *, int);
char * reverse(char *);
void strReverse(char *);
char *strpadleft(char * , char,  int );

int main()
{
  char str1[] = "155122334455",
       str2[] = "12122334455"; //malloc(10);
  int len = strlen(str1) < strlen(str2)?strlen(str2):strlen(str1);
  printf("strlen: %d\n", len);
  // int result = cmp(str1, str2, len);
  // if(result > 0)
  //   printf("%s > %s\n", str1, str2);
  // else if(result < 0)
  //   printf("%s > %s\n", str2, str1);
  // else
  //   printf("%s == %s\n", str1, str2);

    add(str1, str2, len);
    return 0; 
}

int cmp(char *str1, char *str2, int longest) {
    if (strlen(str1) < strlen(str2))
        return -1;
    else if (strlen(str1) > strlen(str2))
        return 1;
    else
        return strncmp(str1, str2, longest);
}

void add(char *str1, char *str2, int longest) {

    char * num1 = strpadleft(str1, '0', longest);
    char * num2 = strpadleft(str2, '0', longest);
    strReverse(num1);
    strReverse(num2);

    char * result = calloc(longest + 2  , sizeof(char));
    int i, x, carry=0;
    for (i = 0; i < longest;i++) {
        x = (num1[i] - '0') + (num2[i] - '0') + carry;

        if (x >= 10) {
            carry = 1;
            x -= 10;
        }
        else {
            carry = 0;
        }
        result[i] = x + '0';
    }

    if (carry == 1) { result[i+1] = '1';}
    strReverse(result);
    printf("Result: %s\n", result );
    //free(result);
    //free(num1);
    //free(num2);
}

char *strpadleft(char * string, char pad, int padSize)
{
    int ssize = strlen(string);
    if (padSize <= ssize) return string;

    char *padded = calloc((padSize + 1) , sizeof(char));
    memset(padded, pad, padSize-ssize);
    padded = strcat(padded, string);
    printf("Old: %s\nNew: %s\n", string, padded);
    return padded;
}

void strReverse(char* str){
    int length = strlen(str);
    char temp;
    int i,j;
    for(i = 0, j = length-1;i < (length-1)/2; i++, j--){
        temp = str[i];
        str[i]=str[j];
        str[j] = temp;
    }
    return;
}

这是我的 valgrind 输出(valgrind 的完整输出位于 http://textsnip.com/ae3c9a，因为它对于 SO 来说太多了):

==17115== Memcheck, a memory error detector
==17115== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==17115== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==17115== Command: a.out
==17115== 
==17115== Conditional jump or move depends on uninitialised value(s)
==17115==    at 0x414F76: __linkin_atfork (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x404383: ptmalloc_init.part.8 (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x407E64: malloc_hook_ini (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x4538E2: _dl_init_paths (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x415788: _dl_non_dynamic_init (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x416002: __libc_init_first (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x40173C: (below main) (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==  Uninitialised value was created
==17115==    at 0x45018A: brk (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x41370B: sbrk (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x401C95: __pthread_initialize_minimal (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x4016F0: (below main) (in /p2/hj/jsiegal/csc352/assg5/a.out)

...

==17115== Use of uninitialised value of size 8
==17115==    at 0x405B27: _int_malloc (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x408E29: calloc (in /p2/hj/jsiegal/csc352/assg5/a.out)
==17115==    by 0x401418: add (strmath.c:51)
==17115==    by 0x4012AB: main (strmath.c:31)
==17115==  Uninitialised value was created by a stack allocation
==17115==    at 0x453ADD: _dl_init_paths (in /p2/hj/jsiegal/csc352/assg5/a.out)

已修复:

/*
 * File: strmath.c
 */

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

int cmp(char *, char *, int);
void add(char *, char *, int);
char * reverse(char *);
void strReverse(char *);
void strpadleft(char * , char *, char,  int );

int main()
{
  char str1[] = "155122334455",
       str2[] = "12122334455"; //malloc(10);
  int len = strlen(str1) < strlen(str2)?strlen(str2):strlen(str1);
  printf("strlen: %d\n", len);
  // int result = cmp(str1, str2, len);
  // if(result > 0)
  //   printf("%s > %s\n", str1, str2);
  // else if(result < 0)
  //   printf("%s > %s\n", str2, str1);
  // else
  //   printf("%s == %s\n", str1, str2);

    add(str1, str2, len);
    return 0; 
}

int cmp(char *str1, char *str2, int longest) {
    if (strlen(str1) < strlen(str2))
        return -1;
    else if (strlen(str1) > strlen(str2))
        return 1;
    else
        return strncmp(str1, str2, longest);
}

void add(char *str1, char *str2, int longest) {

    char * num1 = malloc((longest + 1) * sizeof(char));
    memset(num1, '\0', longest+1);        
    strpadleft(str1, num1, '0', longest);

    char * num2 = malloc((longest + 1) * sizeof(char));
    memset(num2, '\0', longest+1);
    strpadleft(str2, num2, '0', longest);

    strReverse(num1);
    strReverse(num2);

    char * result = malloc(longest + 2  * sizeof(char));
    memset(result, '\0', longest+2);
    int i, x, carry=0;
    for (i = 0; i < longest;i++) {
        x = (num1[i] - '0') + (num2[i] - '0') + carry;

        if (x >= 10) {
            carry = 1;
            x -= 10;
        }
        else {
            carry = 0;
        }
        result[i] = x + '0';
    }

    if (carry == 1) { result[i+1] = '1';}
    strReverse(result);
    printf("Result: %s\n", result );
    free(result);
    free(num1);
    free(num2);
}

void strpadleft(char * string, char *padded, char pad, int padSize)
{
    int ssize = strlen(string);
    if (padSize <= ssize) {
        strcpy(padded, string);
        return;
    }

    //char *padded = malloc((padSize + 1) * sizeof(char));
    //memset(padded, '\0', padSize);
    memset(padded, pad, padSize-ssize);
    padded = strcat(padded, string);
    printf("Old: %s\nNew: %s\n", string, padded);
    return;
}

void strReverse(char* str){
    int length = strlen(str);
    char temp;
    int i,j;
    for(i = 0, j = length-1;i < (length-1)/2; i++, j--){
        temp = str[i];
        str[i]=str[j];
        str[j] = temp;
    }
    return;
}

valgrind 输出:

==12778== Memcheck, a memory error detector
==12778== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==12778== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==12778== Command: a.out
==12778==
strlen: 12
Old: 12122334455
New: 012122334455
Result: 167244668910
==12778==
==12778== HEAP SUMMARY:
==12778==     in use at exit: 0 bytes in 0 blocks
==12778==   total heap usage: 3 allocs, 3 frees, 40 bytes allocated
==12778==
==12778== All heap blocks were freed -- no leaks are possible
==12778==
==12778== For counts of detected and suppressed errors, rerun with: -v
==12778== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)

最佳答案

valgrind 日志并不代表您的程序执行情况。它实际上对 libc 内部函数感到疯狂。造成这种情况的明显原因是缺少针对您正在使用的确切 libc 版本的正确抑制文件(误报内存访问/分配错误列表)。 Valgrind 应该自动解决这个问题，但这并没有发生。您需要在系统中重新编译 valgrind，以便它再次检测到正确的 libc，或者完全无法自动检测它(然后您需要手动构建一个抑制文件)。例如，参见:

还有抑制文件文档:

现在，对于代码来说，很明显每个calloc没有对应的free。我将复制粘贴我的 valgrind 执行，以便您了解真正的 valgrind 输出是什么:

(...)
==26074== 13 bytes in 1 blocks are definitely lost in loss record 1 of 2
==26074==    at 0x4C29E46: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==26074==    by 0x400A15: strpadleft (in /tmp/a)
==26074==    by 0x40081A: add (in /tmp/a)
==26074==    by 0x4007D4: main (in /tmp/a)
==26074== 
==26074== 14 bytes in 1 blocks are definitely lost in loss record 2 of 2
==26074==    at 0x4C29E46: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==26074==    by 0x40084B: add (in /tmp/a)
==26074==    by 0x4007D4: main (in /tmp/a)

这显示了发生的情况:没有 calloc 具有匹配的空闲。在 add 函数中，有一个用于结果的 calloc 。缺少一个免费的。在 strpadleft 中，有一个用于结果函数的 calloc。因此它返回一个动态分配的变量，该变量应该由调用者释放。那个不见了。然而，真正的问题是 strpadleft 可能会提前返回(返回字符串)而不分配任何内容。调用者无法知道该函数是否正在分配新值。这是错误的。要么通知调用者操作完成了什么，要么统一分配(始终分配)。

结论:释放内存是匹配所有分配的简单问题。您可以跟踪变量的分配情况。当您不再需要它们时，释放它们。

关于C 内存错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15056823/

上一篇：c - 查找 C 代码段的运行时间

下一篇：c - C 中的 UDP 套接字 : client1 to server to client2

相关文章：

C++类实例数组初始化

c - 如何实现calloc

c - 为什么 char 指针没有给出段错误？

c++ - 恒定时间访问是否​​意味着在某些时候是连续的内存？

c++ - open( char *filename, int access, int Permission) 在哪里定义的？

performance - 有没有工具可以测量 C 程序中的所有缓存级别？

android - VALGRIND 内部错误 : Valgrind received a signal 11 (SIGSEGV) - exiting

c - 为什么在读取用户输入时，c 中的 scanf 会跳过字符值？

c - 关于 calloc 的奇怪事情

gcc - calloc 崩溃

©2024 IT工具网  联系我们