動態內存：malloc和realloc

Question

我是C語言的新手，使用動態內存時遇到了麻煩。 我為結構圖malloc，然后根據需要重新分配。 在嘗試調試代碼時，我在ddd的幫助下注意到，我覆蓋了上一個圖形（在我提供的第二段代碼中-變量的名稱為FigureHere）。 如果有人能看到我的愚蠢錯誤的成因，請告訴我。

第一個代碼塊在第二個塊中調用void。

#include <assert.h>
#include "draw2.h"
#include "draw2a.h"
#include "draw2b.h"

const char Exec_c[]  = "java -jar Sketchpad.jar";

void parseFile(FILE * fp, FILE *sketcher){ 
    char line [MAX_WORD] = {"NULL"}; 
    char word [MAX_WORD] = {"NULL"};
    char figureName [MAX_WORD] = {"NULL"};
    struct figure *pointsAndname;                     
    int countNumberoffigures = 0;                                   //accounts to which figure in the array we are on
    printOutput();
    int temp = 0;
    pointsAndname = malloc(temp);
    assert(pointsAndname != NULL);
    while ( fgets(line, MAX_WORD - 1, fp) != NULL ){
        int nuRead = sscanf(line, "%s", word);
        assert(pointsAndname != NULL);
        if ( nuRead > 0 ){
            if(strncmp(word, "Figure", MAX_WORD)==0){           //1)reads the figure, name and the two starting points
                countNumberoffigures += 1;                      
                assert(pointsAndname != NULL);
                figureFunction(fp,line, word, figureName, countNumberoffigures, pointsAndname + countNumberoffigures - 1);  
                if (temp <= countNumberoffigures){
                    temp += sizeof(struct figure);
                    pointsAndname = realloc(pointsAndname, temp);
                }
            }                                                 
            if(strncmp(word, "printFigure", MAX_WORD)==0){      //4)read the command printFigure, name of the figure
                printFigure(fp, line, countNumberoffigures, pointsAndname + countNumberoffigures - 1);
            }
            if(strncmp(word, "drawFigure", MAX_WORD)==0){       //5)read the command drawFigure and the name of the figure
                drawFigure(sketcher, line, countNumberoffigures);
            }
            if(strncmp(word, "translate", MAX_WORD)==0){        //6)read the command translate 
                translate(line, sketcher, countNumberoffigures);
            }
            if(strncmp(word, "child", MAX_WORD)==0){            //7)reads command child and the name of the figure
                child(line, word, figureName, sketcher);
            }
            if(strncmp(word, "#", MAX_WORD)==0){                //8)reads the whole line until the \n
                printf(line);
            }
            if(strncmp(word, "end", MAX_WORD)==0){
                fprintf (sketcher, "end\n");
            }
            if(strncmp(word, "rotate", MAX_WORD)==0){
                rotate(line, sketcher, countNumberoffigures);
            }
        }
    }
}

void processArgument(char argument[]){
    FILE *sketcher;
    FILE *fp;
    fp = fopen (argument, "r");
    sketcher = popen(Exec_c, "w");
    if (fp == NULL){
        printf ("Could not open pipe to %s\n", argument);
        exit (EXIT_FAILURE);
    }
    if (sketcher == NULL){
        printf ("Could not open pipe to %s\n", argument);
        exit (EXIT_FAILURE);
    }else{
        parseFile(fp, sketcher);
        if(fclose(fp)==EOF){
            printf("couldn't close pipe to %s.\n", argument);
            exit(EXIT_FAILURE);
        }
        if (pclose(sketcher) == -1){                                                 
            fprintf(stderr, "draw_line error: couldn't close pipe to %s.\n", Exec_c);
            exit(EXIT_FAILURE);    
        }
    }
}

int main (int argc,  char *argv[]){
    int i;
    if ( argc < 2 ){
        printf ("%s\n", "0 comment(s)");
        exit(EXIT_FAILURE);
    }else{
        for (i = 1; i < argc; i++){
            processArgument(argv[i]);
        }
    }
    return 0;
}

---

#include "draw2.h"
#include "draw2a.h"

void printOutput(){
    printf("./draw2 started on:");

    fflush(stdout);
    system("date\n");
}
/*send what ever there is after the child to sketchpad(in that specific line)*/
void child (char line[], char word[], char nameFigure[], FILE * sketcher){          
    sscanf(line, "%s%s", word, nameFigure);
    fprintf (sketcher, "%s\n", &line[6]);
} 

/*I construct the struct by reading from the Figure line to the end figure line.*/
void figureFunction (FILE * fp, char line[], char word[], char figureName[], int countNumberoffigures, struct figure *figureHere){
    double startx, starty;
    int temp = 0;
    printf("The line: %s", line);

    figureHere->vertices = malloc(temp);
    sscanf(line, "%s%s%lf%lf%*s", word, figureHere->figureName, &startx, &starty);
    (*(figureHere->vertices)).x = startx;              
    (*(figureHere->vertices)).y = starty;
    printf("I'm in side figureFunction and this is my figureHere->figureName = %s\n\n", figureHere->figureName);
    fgets(line, MAX_WORD - 1, fp);                  
    int nuRead = sscanf(line, "%s", word);              //until the line with End Figure I construct my points of figure.
    int i = 1;                                                     
    while (strncmp(word, "End", MAX_WORD)!=0){ 
        if (strncmp(word, "#", MAX_WORD) == 0){
            printf("%s",line);
        }           
        if (strncmp(word, "draw", MAX_WORD) == 0){
            sscanf (line, "%s%lf%lf", word, &startx, &starty);
            figureHere->vertices[i].x = figureHere->vertices[i-1].x + startx;
            figureHere->vertices[i].y = figureHere->vertices[i-1].y + starty;
            i += 1;
        }
        fgets(line, MAX_WORD - 1, fp);
        nuRead = sscanf(line, "%s", word);
    }                                          
    figureHere->countPoints = i;
    if (temp >= figureHere->countPoints){
        temp += sizeof(struct pointxy);
        figureHere->vertices = realloc(figureHere->vertices, temp);
    }                        
}

---

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

void parseFile(FILE * fp, FILE * sketcher); 
void processArgument(char argument[]);
void printOutput();

#define MAX_WORD 256
#define initial_size 17

extern const char argument[];

/* prototypes for non-c99 library functions */
FILE* popen(const char*, const char*);
int pclose(FILE*);
struct pointxy {
    double x;
    double y;
};

struct figure{
    //struct figure *nextfigure;

    char figureName[MAX_WORD];
    struct pointxy *vertices;
    int countPoints;
};

struct figure *figurehere;

Answer 1

保羅

您的初始malloc（）大小為零； 您至少需要一個要素才能開始。 最重要的是，您正在反向進行此操作。 您試圖在分配用於容納它們的空間之前將值分配給figHere。 您需要確定結構中需要多少個新值，然后調用malloc（）或將realloc（）代碼放入if（strncmp（word，“ draw”，MAX_WORD）== 0）部分：

if (strncmp(word, "draw", MAX_WORD) == 0){
    temp += sizeof(struct pointxy);
    figureHere->vertices = realloc(figureHere->vertices, temp);
    sscanf (line, "%s%lf%lf", word, &startx, &starty);
    figureHere->vertices[i].x = figureHere->vertices[i-1].x + startx;
    figureHere->vertices[i].y = figureHere->vertices[i-1].y + starty;
    i += 1;
}

Answer 2

void figureFunction (FILE * fp, char line[], char word[], char figureName[], int countNumberoffigures, struct figure *figureHere){
    /* ... */
    int temp = 0;
    /* ... */
    figureHere->vertices = malloc(temp);

temp為0

    /* ... */
    int nuRead = sscanf(line, "%s", word);              //until the line with End Figure I construct my points of figure.
    int i = 1;                                                     
    while (strncmp(word, "End", MAX_WORD)!=0){ 
        /* ... */
        if (strncmp(word, "draw", MAX_WORD) == 0){
            sscanf (line, "%s%lf%lf", word, &startx, &starty);
            figureHere->vertices[i].x = figureHere->vertices[i-1].x + startx;

不不不。 figureHere->vertices[1]不存在

            figureHere->vertices[i].y = figureHere->vertices[i-1].y + starty;
            i += 1;
        }
        fgets(line, MAX_WORD - 1, fp);
        nuRead = sscanf(line, "%s", word);
    }
    /* ... */
}