c - 我的 C 代码有什么问题？

Question

当我调用 print_token() 时，我的应用程序崩溃了。我花了一整天试图解决这个问题，但没有成功，我放弃了。帮助。

//#include "memory.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

    struct TOKEN
    {
            int type;
            char *str;
    };

#define TOKEN_SIZE sizeof(struct TOKEN)

struct TOKEN *ini;
struct TOKEN *cur;
struct TOKEN *end;

int size = TOKEN_SIZE * 1;

void init_token_buffer(void);
void save_token(int type, const char *str);
void print_tokens(void);

void init_token_buffer(void)
{
    ini = (struct TOKEN*) malloc(size); // 8 bytes...
    cur = ini;
    end = ini + size;
}

void save_token(int type, const char *str)
{
    printf("cur == end : %d\n", cur == end);

    if (cur == end)
    {
        int lastSize = (end - ini);
        int  newSize = size + lastSize;
        ini = (struct TOKEN*) realloc(ini, newSize); // 16,24,32...
        end = ini +  newSize;
        cur = ini + lastSize;

        printf("l:%d, n:%d\n", lastSize, newSize);
    }

    int  strSize = strlen(str) * sizeof(char) + sizeof(char);
    char *newStr = (char*) malloc(strSize);

    cur->str  = (char*) memcpy(newStr, str, strSize);
    cur->type = type;

    printf("string:%s, type:%X\n", cur->str, cur->type);
    // here it prints right!
    cur += TOKEN_SIZE;
}

void print_tokens()
{
    int i;
    int total = (cur - ini);

    printf("\ntotal tokens:%d\n", total / TOKEN_SIZE);
    printf("total  bytes:%d\n", total);

    for (i = 0; i < total; i += TOKEN_SIZE)
    {
        struct TOKEN *t = &ini[i];
        printf("string:%s, type:%X\n", t->str, t->type);
        // here it crashes at the 2º loop! (ini[8])
    }
}

您可以测试为:

main() {
    init_token_buffer();
    save_token(0, "aaa");
    save_token(0, "bbb");
    save_token(0, "ccc");
    save_token(0, "ddd");
    print_tokens();
}

Answer 1

以下两点是你的错误:

1. i += TOKEN_SIZE
2. &ini[i]

因为ini是TOKEN *类型，它的访问索引是sizeof TOKEN的倍数。你要了解pointer arithmetics .

我还建议您至少查看编译器警告:

$ gcc -Wall -pedantic -o test ./test.c 
./test.c: In function ‘init_token_buffer’:
./test.c:26:38: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
./test.c:26:38: warning: (this will be reported only once per input file) [enabled by default]
./test.c: In function ‘save_token’:
./test.c:46:2: warning: ISO C90 forbids mixed declarations and code [-pedantic]
./test.c: In function ‘print_tokens’:
./test.c:62:40: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long unsigned int’ [-Wformat]
./test.c: In function ‘main’:
./test.c:81:1: warning: control reaches end of non-void function [-Wreturn-type]

...并可能使用 valgrind 或类似工具来检查程序是否存在运行时错误:

$ valgrind ./test 
==9732== Memcheck, a memory error detector
==9732== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==9732== Using Valgrind-3.6.1-Debian and LibVEX; rerun with -h for copyright info
==9732== Command: ./test
==9732== 
cur == end : 0
string:aaa, type:0
cur == end : 1
l:16, n:32
==9732== Invalid write of size 8
==9732==    at 0x400769: save_token (in /tmp/test)
==9732==    by 0x40089B: main (in /tmp/test)
==9732==  Address 0x51ce1e8 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid write of size 4
==9732==    at 0x400777: save_token (in /tmp/test)
==9732==    by 0x40089B: main (in /tmp/test)
==9732==  Address 0x51ce1e0 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 4
==9732==    at 0x400780: save_token (in /tmp/test)
==9732==    by 0x40089B: main (in /tmp/test)
==9732==  Address 0x51ce1e0 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 8
==9732==    at 0x400789: save_token (in /tmp/test)
==9732==    by 0x40089B: main (in /tmp/test)
==9732==  Address 0x51ce1e8 is not stack'd, malloc'd or (recently) free'd
==9732== 
string:bbb, type:0
cur == end : 1
l:32, n:48
==9732== Invalid write of size 8
==9732==    at 0x400769: save_token (in /tmp/test)
==9732==    by 0x4008AA: main (in /tmp/test)
==9732==  Address 0x51ce398 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid write of size 4
==9732==    at 0x400777: save_token (in /tmp/test)
==9732==    by 0x4008AA: main (in /tmp/test)
==9732==  Address 0x51ce390 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 4
==9732==    at 0x400780: save_token (in /tmp/test)
==9732==    by 0x4008AA: main (in /tmp/test)
==9732==  Address 0x51ce390 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 8
==9732==    at 0x400789: save_token (in /tmp/test)
==9732==    by 0x4008AA: main (in /tmp/test)
==9732==  Address 0x51ce398 is not stack'd, malloc'd or (recently) free'd
==9732== 
string:ccc, type:0
cur == end : 1
l:48, n:64
==9732== Invalid write of size 8
==9732==    at 0x400769: save_token (in /tmp/test)
==9732==    by 0x4008B9: main (in /tmp/test)
==9732==  Address 0x51ce558 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid write of size 4
==9732==    at 0x400777: save_token (in /tmp/test)
==9732==    by 0x4008B9: main (in /tmp/test)
==9732==  Address 0x51ce550 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 4
==9732==    at 0x400780: save_token (in /tmp/test)
==9732==    by 0x4008B9: main (in /tmp/test)
==9732==  Address 0x51ce550 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 8
==9732==    at 0x400789: save_token (in /tmp/test)
==9732==    by 0x4008B9: main (in /tmp/test)
==9732==  Address 0x51ce558 is not stack'd, malloc'd or (recently) free'd
==9732== 
string:ddd, type:0

total tokens:4
total  bytes:64
string:aaa, type:0
==9732== Invalid read of size 4
==9732==    at 0x400843: print_tokens (in /tmp/test)
==9732==    by 0x4008BE: main (in /tmp/test)
==9732==  Address 0x51ce350 is not stack'd, malloc'd or (recently) free'd
==9732== 
==9732== Invalid read of size 8
==9732==    at 0x400849: print_tokens (in /tmp/test)
==9732==    by 0x4008BE: main (in /tmp/test)
==9732==  Address 0x51ce358 is not stack'd, malloc'd or (recently) free'd
==9732== 
string:(null), type:0
string:(null), type:0
string:ddd, type:0
==9732== 
==9732== HEAP SUMMARY:
==9732==     in use at exit: 80 bytes in 5 blocks
==9732==   total heap usage: 8 allocs, 3 frees, 176 bytes allocated
==9732== 
==9732== LEAK SUMMARY:
==9732==    definitely lost: 12 bytes in 3 blocks
==9732==    indirectly lost: 0 bytes in 0 blocks
==9732==      possibly lost: 0 bytes in 0 blocks
==9732==    still reachable: 68 bytes in 2 blocks
==9732==         suppressed: 0 bytes in 0 blocks
==9732== Rerun with --leak-check=full to see details of leaked memory
==9732== 
==9732== For counts of detected and suppressed errors, rerun with: -v
==9732== ERROR SUMMARY: 18 errors from 14 contexts (suppressed: 4 from 4)

您的程序可能如下所示:

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

struct TOKEN
{
    int type;
    char *str;
};

struct TOKEN *ini = NULL;
struct TOKEN *cur = NULL;
struct TOKEN *end = NULL;

static void save_token(int type, const char *str)
{
    struct TOKEN *p;
    size_t n;
    char *s;

    if (cur == end) {
        n = (size_t)(end - ini) + 1;
        p = realloc(ini, n * sizeof(struct TOKEN));
        if (!p) {
            /* Out of memory??? */
            abort();
        }
        cur = p + (cur - ini);
        ini = p;
        end = p + n;
    }

    if (!(s = strdup(str))) {
            /* SOS! */
            abort();
    }

    cur->str = s;
    cur->type = type;
    ++cur;
}

static void print_tokens()
{
    struct TOKEN *i = ini;
    struct TOKEN *e = end;

    printf("Total tokens: %ld\n", (e - i));
    printf("Total bytes: %ld\n", (e - i) * sizeof(struct TOKEN));

    while (i < e) {
        printf("string:%s, type:%X\n", i->str, i->type);
        ++i;
    }
}

static void clear_tokens()
{
    struct TOKEN *i = ini;
    struct TOKEN *e = end;

    if (!ini)
        return;

    while (i < e) {
        if (i->str)
            free(i->str);
        ++i;
    }

    free(ini);
    ini = cur = end = NULL;
}

int main() {
    save_token(0, "aaa");
    save_token(1, "bbb");
    save_token(2, "ccc");
    save_token(3, "ddd");
    print_tokens();
    clear_tokens(); /* Do not forget to clean up resources! */
    return 0;
}

我感谢你为学习 C 所做的努力。虽然你的代码看起来部分是 C99，部分是 ANSI C 之前的部分，部分是 C++ :-D 我建议你买一些好的 C 书，并首先摆脱 IDE ，它站在你和编译器之间。当然，您仍然可以将它用作编辑器，但请尝试使用命令行工具进行编译并了解发生了什么......

祝你好运!