c - 释放为 C 中的一个很长的字符串 (char*) 分配的内存？

Question

拜托，我需要帮助来释放分配给一个非常长的字符串的内存。我试图将代码缩减为包含我遇到的问题的这个小片段:

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

#define N 6
#define E 1024

int M[N][N][N], R[N*N][N], C[N*N][N], F[N*N][N];

void init_rcf() {
    int i, j, k, p;

    p = 0;
    for(j=0; j<N; j++) {
        for(k=0; k<N; k++) {
            for(i=0; i<N; i++) 
                R[p][i] = M[i][j][k];
            p++;
        }
    }

    p = 0;
    for(i=0; i<N; i++) {
        for(k=0; k<N; k++) {
            for(j=0; j<N; j++)
                C[p][j] = M[i][j][k];
            p++;
        }
    }

    p = 0;
    for(i=0; i<N; i++) {
        for(j=0; j<N; j++) {
            for(k=0; k<N; k++)
                F[p][k] = M[i][j][k];
            p++;
        }
    }
}

char *bin(int n, int p) {
    int c, d, count;
    char *pointer;
    count = 0;
    pointer = (char*)malloc(p+1);

    for (c = p-1;c >= 0;c--) {
        d = n >> c;
        if (d & 1) 
            *(pointer+count) = 1 + '0';
        else 
            *(pointer+count) = 0 + '0';
        count++;
    }
    *(pointer+count) = '\0';
    return  pointer;
}

int f0(int n) {
    return ceil(log2(n+1)); 
}

int f1() {
    int sum, max = 0;
    for(int k=0;k<N;k++) {
        for(int j=0;j<N;j++) {
            for(int i=0;i<N-1;i++) {
                sum = M[i][j][k] + M[i+1][j][k]; 
                if (sum > max) 
                    max = sum; 
            }
        }   
    }
    return max;
}

int f2() {
    int sum, max = 0;
    for(int k=0;k<N;k++) {
        for(int i=0;i<N;i++) {
            for(int j=0;j<N-1;j++) {
                sum = M[i][j][k] + M[i][j+1][k]; 
                if (sum > max) 
                    max = sum; 
            }
        }   
    }
    return max;
}

int f3() {
    int sum, max = 0;
    for(int j=0;j<N;j++) {
        for(int i=0;i<N;i++) {
            for(int k=0;k<N-1;k++) {
                sum = M[i][j][k] + M[i][j][k+1]; 
                if (sum > max) 
                    max = sum; 
            }
        }   
    }
    return max;
}

int f4() {
    int m1 = f1(),  m2 = f2(), m3 = f3(); 
    if ((m1 >= m2) && (m1 >= m3)) return m1;
    if ((m1 <= m2) && (m2 >= m3)) return m2;
    if ((m1 <= m3) && (m2 <= m3)) return m3;
}

char *g_fxn() {
    char *g = (char *) malloc(1 + (N*N*N)*3); 
    int k = f0(f4());

    init_rcf();
    strcpy(g,"");            
    for(int i=0; i<N*N; i++) 
        for(int j=0; j<N; j++) 
            strcat(g,bin(R[i][j],k));
    for(int i=0; i<N*N; i++) 
        for(int j=0; j<N; j++) 
            strcat(g,bin(C[i][j],k));
    for(int i=0; i<N*N; i++) 
        for(int j=0; j<N; j++) 
            strcat(g,bin(F[i][j],k));
    return g;
}

void convert2bin(char *file_in) {
    const char *FILENAME_IN = file_in;
    const char FILENAME_OUT[] = "temp.txt";
    char c, d; 
    int k=0;

    FILE *infile;
    FILE *outfile;

    infile = fopen(FILENAME_IN, "rb");
    outfile = fopen(FILENAME_OUT, "w");
    if(infile == NULL){
        fprintf(stderr, "Error: Source file not found.\n");
        exit(EXIT_FAILURE);
    }

    while((c = fgetc(infile)) != EOF){
        k++;
        unsigned n = (sizeof(c) * CHAR_BIT) - 1; 
        for (int i=0; i<=n; i++) { 
            int m = (c >> (n-i)) & 1; 
            d = '0'+m;          
            fwrite(&d, 1, sizeof(d), outfile);
        }
    }

    if (k < E) {
        d = '1';
        fwrite(&d, 1, sizeof(d), outfile);
        for (int i=k; i<=E; i++) { 
            d = '0';            
            fwrite(&d, 1, sizeof(d), outfile);
        }
    }

    fclose(infile);
    fclose(outfile);
}

void digest() {
    const char *FILENAME_IN = "temp.txt";
    const char FILENAME_OUT[] = "digest.txt";

    int size = N*N*N; // size of message to construct N*N*N matrix
    char c, msg0[size], *msgf; 

    FILE *infile;
    FILE *outfile;

    infile = fopen(FILENAME_IN, "r");
    outfile = fopen(FILENAME_OUT, "wb");
    if(infile == NULL){
        fprintf(stderr, "Error: Source file \"temp.txt\" not found.\n");
        exit(EXIT_FAILURE);
    }

    int quit = 0;
    while (quit == 0) {
        msgf = (char *) malloc(1 + (size)*3);
        strcpy(msgf, ""); 
        strcpy(msg0, "");
        int p = 0;
        while(((c = fgetc(infile)) != EOF) && (p < size)) {
            msg0[p++] = c;
        }

        if(c == EOF) quit = 1;
        if (p > 0) {
            if (p < size) {
                msg0[p] = '1';
                for(int i=p+1; i<size; i++) 
                    msg0[i] = '0';
            }

            for (int k=0; k<N; k++)
                for (int j=0; j<N; j++)
                    for (int i=0; i<N; i++) {
                        c = msg0[i + N * (j + N * k)];
                        if (c == '0')
                            M[i][j][k] = 0;
                        else 
                            M[i][j][k] = 1;
                    }

            strcpy(msgf, g_fxn());             
            int q = 0;

            while (q<strlen(msgf)) {
                int d;
                char b = 0;
                for (int r=0; r<8; r++) {
                    if (msgf[q++] == '0') 
                        d = 0;
                    else 
                        d = 1;
                    b = ((b<<1) | d);
                }
                fwrite(&b, 1, 1, outfile);
                b = 0;
            }
        }
    }

    free(msgf);
    fclose(infile);
    fclose(outfile);
}

int main(int argc, char *argv[]){
    if (argc!=2) {
        fprintf(stderr, "Error: Provide name of one source file.\n");
        exit(EXIT_FAILURE);
    }

    char *clear_file = argv[1];

    convert2bin(clear_file);

    digest();

    printf("File successfully digested!\n");

    return(0);
}

此代码适用于最多 27 个字节的输入文件，但超过 27 个字节时每次都会崩溃。

尝试调试后，我发现问题出在 strcpy(msgf, g_fxn()); 对函数 g_fxn 的调用上，我的猜测是问题出现了来自为消息分配的大块内存，但之后似乎没有被释放。我猜这是因为当对 g_fxn 的调用较少但调用较多时代码会崩溃。

有人知道我该如何解决这个问题吗？

Answer 1

msgf 多次在函数 digest() 的 while 循环中分配:

msgf = (char *) malloc(1 + (size)*3);

但是 free() 只在循环后被调用一次:

free(msgf);

这至少是我发现的一个内存泄漏。