c - 有关malloc和free的帮助:检测到Glibc:free():无效的指针

我需要帮助调试这段代码。我知道问题出在malloc和free，但找不到确切的位置，原因和如何解决它。请不要回答：“使用gdb”，就这样。我会使用gdb来调试它，但是我对它还不太了解，并且还在学习它，同时，我希望有另一个解决方案。
谢谢。

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>

#define MAX_COMMAND_LENGTH  256
#define MAX_ARGS_NUMBER     128
#define MAX_HISTORY_NUMBER  100

#define PROMPT ">>> "

int num_elems;

typedef enum {false, true} bool;

typedef struct {
    char **arg;
    char *infile;
    char *outfile;
    int background;
} Command_Info;

int parse_cmd(char *cmd_line, Command_Info *cmd_info)
{
    char *arg;
    char *args[MAX_ARGS_NUMBER];

    int i = 0;
    arg = strtok(cmd_line, " ");
    while (arg != NULL) {
        args[i] = arg;
        arg = strtok(NULL, " ");
        i++;
    }

    num_elems = i;precisa em free_mem
    if (num_elems == 0)
        return 0;

    cmd_info->arg = (char **) ( malloc(num_elems * sizeof(char *)) );
    cmd_info->infile = NULL;
    cmd_info->outfile = NULL;
    cmd_info->background = 0;

    bool b_infile = false;
    bool b_outfile = false;

    int iarg = 0;
    for (i = 0; i < num_elems; i++)
    {
        if ( !strcmp(args[i], "<") )
        {
            if ( b_infile || i == num_elems-1 || !strcmp(args[i+1], "<") || !strcmp(args[i+1], ">") || !strcmp(args[i+1], "&") )
                return -1;

            i++;
            cmd_info->infile = malloc(strlen(args[i]) * sizeof(char));
            strcpy(cmd_info->infile, args[i]);
            b_infile = true;
        }

        else if (!strcmp(args[i], ">"))
        {
            if ( b_outfile || i == num_elems-1 || !strcmp(args[i+1], ">") || !strcmp(args[i+1], "<") || !strcmp(args[i+1], "&") )
                return -1;

            i++;
            cmd_info->outfile = malloc(strlen(args[i]) * sizeof(char));
            strcpy(cmd_info->outfile, args[i]);
            b_outfile = true;
        }

        else if (!strcmp(args[i], "&"))
        {
            if ( i == 0 || i != num_elems-1 || cmd_info->background )
                return -1;

            cmd_info->background = true;
        }

        else
        {
            cmd_info->arg[iarg] = malloc(strlen(args[i]) * sizeof(char));
            strcpy(cmd_info->arg[iarg], args[i]);
            iarg++;
        }
    }

    cmd_info->arg[iarg] = NULL;

    return 0;
}


void print_cmd(Command_Info *cmd_info)
{
    int i;
    for (i = 0; cmd_info->arg[i] != NULL; i++)
        printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]);
    printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]);
    printf("infile=\"%s\"\n", cmd_info->infile);
    printf("outfile=\"%s\"\n", cmd_info->outfile);
    printf("background=\"%d\"\n", cmd_info->background);
}

void get_cmd(char* str)
{
    fgets(str, MAX_COMMAND_LENGTH, stdin);
    str[strlen(str)-1] = '\0';
}

pid_t exec_simple(Command_Info *cmd_info)
{
    pid_t pid = fork();

    if (pid < 0)
    {
        perror("Fork Error");
        return -1;
    }

    if (pid == 0)
    {
        if ( (execvp(cmd_info->arg[0], cmd_info->arg)) == -1)
        {
            perror(cmd_info->arg[0]);
            exit(1);
        }
    }

    return pid;
}

void type_prompt(void)
{
    printf("%s", PROMPT);
}

void syntax_error(void)
{
    printf("msh syntax error\n");
}

void free_mem(Command_Info *cmd_info)
{
    int i;
    for (i = 0; cmd_info->arg[i] != NULL; i++)
        free(cmd_info->arg[i]);
    free(cmd_info->arg);
    free(cmd_info->infile);
    free(cmd_info->outfile);
}

int main(int argc, char* argv[])
{
    char cmd_line[MAX_COMMAND_LENGTH];
    Command_Info cmd_info;
    //char* history[MAX_HISTORY_NUMBER];

    while (true)
    {
        type_prompt();

        get_cmd(cmd_line);

        if ( parse_cmd(cmd_line, &cmd_info) == -1)
        {
            syntax_error();
            continue;
        }

        if (!strcmp(cmd_line, ""))
            continue;

        if (!strcmp(cmd_info.arg[0], "exit"))
            exit(0);

        pid_t pid = exec_simple(&cmd_info);

        waitpid(pid, NULL, 0);

        free_mem(&cmd_info);
    }

    return 0;
}

最佳答案

因为C中的字符串以空结尾，所以它们在内存中的实际大小是length+1，而不是

cmd_info->infile = malloc(strlen(args[i]) * sizeof(char));

你应该有

cmd_info->infile = malloc((strlen(args[i])+1) * sizeof(char));

编辑：正如Aeth所说，您需要更改malloc的每一次出现，以包含该附加空字符的空间：

cmd_info->arg = (char **) ( malloc(num_elems * sizeof(char *)) ); //this one can stay, since it determines number of strings, not string length
cmd_info->outfile = malloc((strlen(args[i])+1) * sizeof(char));
cmd_info->arg[iarg] = malloc((strlen(args[i])+1) * sizeof(char));

关于c - 有关malloc和free的帮助:检测到Glibc:free():无效的指针，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/2658648/