我正在做一个学校项目，我必须将 PPM 数据存储到结构中。我对结构内的字符串数组有疑问。
typedef struct {
char **comments;
} PPM;
我有 3 个使用此结构的函数。
PPM *getPPM() 用于从文件中获取所有 PPM 数据并将其存储到结构中
void showPPM(PPM * img)在终端显示图像数据
PPM *encode(PPM *img) 用于改变图像RGB值的LSB
问题是 getPPM 按预期工作并将所有评论获取到 getPPM 的评论数组中。如果我这样做，它会很好地显示它们:
PPM *p = getPPM(fin);
showPPM(p);
但是如果我尝试使用这样的编码函数调用它:
PPM *p = getPPM(fin);
PPM *g = encode(p);
showPPM(g);
调试器显示，一旦程序进入encode 函数，注释值就会重置为 NULL，即使此函数甚至没有触及注释。是我调用这些函数的方式有误还是我的代码有问题？如果问题不是调用函数的方式，我将尝试提供最少的代码，因为代码很大而且一切都相互依赖。
我是 C 语言的新手。我尝试了数小时来了解问题，但无法在任何地方找到解决方案。任何帮助将不胜感激。
编辑:这是我能做的最小的。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//Structures
typedef struct {
int r, g, b;
} pixels;
typedef struct {
char format[3];
char **comments;
int width, height, maxColors, commentCounter;
pixels **pixelValues;
} PPM;
// Functions declarations
PPM *getPPM(FILE * f);
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret);
void showPPM(PPM * im);
static int *decimalToBinary(const char *message, unsigned int length);
// Main method
int main(int argc, char **argv) {
FILE * fin = fopen(argv[1], "r");
if(fin == NULL) {
perror("Cannot open file");
exit(1);
}
PPM *p = getPPM(fin);
PPM *g = encode(p, "test", 5, 1);
showPPM(g);
return 0;
}
/*
* This function is used to get the image data from a file and populate
* our strutures with it.
*/
PPM *getPPM(FILE * f) {
// Allocate the memory for structure and check if it was successful
PPM *pic = (PPM *) malloc(sizeof(PPM));
if(!pic) {
perror("Unable to allocate memory for structure");
exit(1);
}
char line[100]; // Expecting no more than 100 characters per line.
pic->commentCounter = 0; // This is the counter to keep size if there are more than one comments
int pixelsCounter = 0; // Counter for pixels' array
pic->comments = malloc(sizeof(char *));
pic->pixelValues = malloc(sizeof(PPM));
int lineCounter = 0;
if((pic->comments) == NULL) {
perror("Unable to allocate memory for pixels");
exit(1);
}
while(fgets(line, sizeof(line), f)) {
// Reference: https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input
size_t length = strlen(line);
if(length > 0 && line[length-1] == '\n') {
line[--length] = '\0';
}
// Assigning the file format
if(line[0] == 'P') {
pic->format[0] = line[0];
pic->format[1] = line[1];
pic->format[2] = '\0';
}
//Populate comments into struct PPM
if(line[0] == '#') {
// Reallocate/allocate the array size each time a new line of comment is found
if(pic->commentCounter != 0) {
pic->comments = realloc(pic->comments, (pic->commentCounter+1) * sizeof(char *));
}
// Allocate the memory for the string
pic->comments[pic->commentCounter] = malloc(100 * sizeof(char));
// Write the at commentCounter position of the array; character by character
int i = 0;
while(line[i] != '\0') {
pic->comments[pic->commentCounter][i] = line[i];
i++;
}
pic->comments[pic->commentCounter][i] = '\0';
pic->commentCounter++;
}
/*
* Loading the max color property of the file which is gonna be 3 letters (Usually 255)
* and checking if we previously got maxColors in our construct or not. If we didn't
* then we load this value into the consturct and the condition will never validate
* throughout the iterations
*/
if(strlen(line) == 3 && pic->maxColors == 0 && line[0] != '#') {
pic->maxColors = atoi(line);
continue;
}
/*
* Check if the length of string > 3, which means it is going to be a
* number, potentially RGB value or a comment. But since width & height
* comes before RGB values, our condition will fail once we have found
* the width/height for the next iteration. That's why this condition
* only checks if it is a comment or a numbered value of length > 3
*/
if((strlen(line) > 3) && (pic->width == 0) && (line[0] != '#')) {
char *width = strtok(line, " ");
char *height = strtok(NULL, " ");
pic->width = atoi(width);
pic->height = atoi(height);
continue;
}
/*
* If the width/height and maxColors have been found, that means every
* other line is either going to be the RGB values or a comment.
*/
if((pic->width != 0) && (pic->maxColors != 0) && (line[0] != '#')) {
// length(line) > 3 means all the RGB values are in same line
if(strlen(line) > 3) {
char *val1 = strtok(line, " ");
char *val2 = strtok(NULL, " ");
char *val3 = strtok(NULL, " ");
// pixelsCounter = 0 means it's the first element.
if(pixelsCounter != 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(val1);
pic->pixelValues[pixelsCounter]->g = atoi(val2);
pic->pixelValues[pixelsCounter]->b = atoi(val3);
pixelsCounter++;
} else if(strlen(line) <= 3) {
/*
* If each individual RGB values are in a separete lines, we will
* use a switch case and a line counter to keep track of where the
* values were inserted and when to know when we got RGB values for
* one pixel
*/
if(pixelsCounter != 0 && lineCounter == 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
switch(lineCounter) {
case 0 :
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(line);
lineCounter++;
continue;
case 1 :
pic->pixelValues[pixelsCounter]->g = atoi(line);
lineCounter++;
continue;
case 2 :
pic->pixelValues[pixelsCounter]->b = atoi(line);
lineCounter=0;
pixelsCounter++;
continue;
default:
continue;
}
}
}
}
pic->pixelValues[pixelsCounter] = NULL;
fclose(f);
return pic;
}
void showPPM(PPM * im) {
printf("%s\n",im->format);
int k = 0;
while(k < im->commentCounter) {
printf("%s\n", im->comments[k]);
k++;
}
printf("%d %d\n", im->width, im->height);
printf("%d\n",im->maxColors);
int j = 0;
while(im->pixelValues[j] != NULL) {
printf("%d %d %d\n", im->pixelValues[j]->r, im->pixelValues[j]->g, im->pixelValues[j]->b);
j++;
}
}
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret) {
int *binaryMessage = decimalToBinary(message, mSize);
int i, j = 0, lineCounter = 0;
for(i = 0; i < 40; i++) {
switch(lineCounter) {
case 0 :
im->pixelValues[j]->r |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 1 :
im->pixelValues[j]->g |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 2 :
im->pixelValues[j]->b |= binaryMessage[i] << 0;
lineCounter=0;
j++;
continue;
default:
continue;
}
}
return im;
}
/*
* Converts a string into binary to be used in encode function. It
* first converts each letter of the string into ascii code. Then
* finds and stores each of the 8 bits of that int (ascii code of
* the letter) sequentially in an array.
*/
static int *decimalToBinary(const char *message, unsigned int length) {
/*
* malloc is used here instead of [] notation to allocate memory,
* because defining the variable with [] will make its scope
* limited to this function only. Since we want to access this
* array later on, we use malloc to assign space in the memory
* for it so we can access it using a pointer later on.
*/
int k=0, i, j;
unsigned int c;
unsigned int *binary = malloc(8 * length);
for(i = 0; i < length; i++) {
c = message[i];
for(j = 7; j >= 0; j--,k++) {
/*
* We check here if the jth bit of the number is 1 or 0
* using the bit operator &. If it is 1, it will return
* 1 because 1 & 1 will be true. Otherwise 0.
*/
if((c >> j) & 1)
binary[k] = 1;
else
binary[k] = 0;
}
}
return binary;
}
PPM 文件:
P3
# CREATOR: GIMP PNM Filter Version 1.1
# Amazing comment 2
# Yet another amazing comment
400 530
255
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
最佳答案
在decimalToBinar
unsigned int *binary = malloc(8 * length);
必须是
unsigned int *binary = malloc(8 * length * sizeof(int));
新代码是:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//Structures
typedef struct {
int r, g, b;
} pixels;
typedef struct {
char format[3];
char **comments;
int width, height, maxColors, commentCounter;
pixels **pixelValues;
} PPM;
// Functions declarations
PPM *getPPM(FILE * f);
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret);
void showPPM(PPM * im);
static int *decimalToBinary(const char *message, unsigned int length);
// Main method
int main(int argc, char **argv) {
FILE * fin = fopen(argv[1], "r");
if(fin == NULL) {
perror("Cannot open file");
exit(1);
}
PPM *p = getPPM(fin);
PPM *g = encode(p, "test", 5, 1);
showPPM(g);
free(p->comments);
free(p);
return 0;
}
/*
* This function is used to get the image data from a file and populate
* our strutures with it.
*/
PPM *getPPM(FILE * f) {
// Allocate the memory for structure and check if it was successful
PPM *pic = (PPM *) malloc(sizeof(PPM));
if(!pic) {
perror("Unable to allocate memory for structure");
exit(1);
}
char line[100]; // Expecting no more than 100 characters per line.
pic->commentCounter = 0; // This is the counter to keep size if there are more than one comments
int pixelsCounter = 0; // Counter for pixels' array
pic->comments = malloc(sizeof(char *));
pic->pixelValues = malloc(sizeof(PPM));
int lineCounter = 0;
if((pic->comments) == NULL) {
perror("Unable to allocate memory for pixels");
exit(1);
}
pic->width = 0;
pic->height = 0;
pic->maxColors = 0;
while(fgets(line, sizeof(line), f)) {
// Reference: https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input
size_t length = strlen(line);
if(length > 0 && line[length-1] == '\n') {
line[--length] = '\0';
}
// Assigning the file format
if(line[0] == 'P') {
pic->format[0] = line[0];
pic->format[1] = line[1];
pic->format[2] = '\0';
}
//Populate comments into struct PPM
if(line[0] == '#') {
// Reallocate/allocate the array size each time a new line of comment is found
if(pic->commentCounter != 0) {
pic->comments = realloc(pic->comments, (pic->commentCounter+1) * sizeof(char *));
}
// Allocate the memory for the string
pic->comments[pic->commentCounter] = malloc(100 * sizeof(char));
// Write the at commentCounter position of the array; character by character
int i = 0;
while(line[i] != '\0') {
pic->comments[pic->commentCounter][i] = line[i];
i++;
}
pic->comments[pic->commentCounter][i] = '\0';
pic->commentCounter++;
}
/*
* Loading the max color property of the file which is gonna be 3 letters (Usually 255)
* and checking if we previously got maxColors in our construct or not. If we didn't
* then we load this value into the consturct and the condition will never validate
* throughout the iterations
*/
if(strlen(line) == 3 && pic->maxColors == 0 && line[0] != '#') {
pic->maxColors = atoi(line);
continue;
}
/*
* Check if the length of string > 3, which means it is going to be a
* number, potentially RGB value or a comment. But since width & height
* comes before RGB values, our condition will fail once we have found
* the width/height for the next iteration. That's why this condition
* only checks if it is a comment or a numbered value of length > 3
*/
if((strlen(line) > 3) && (pic->width == 0) && (line[0] != '#')) {
char *width = strtok(line, " ");
char *height = strtok(NULL, " ");
pic->width = atoi(width);
pic->height = atoi(height);
continue;
}
/*
* If the width/height and maxColors have been found, that means every
* other line is either going to be the RGB values or a comment.
*/
if((pic->width != 0) && (pic->maxColors != 0) && (line[0] != '#')) {
// length(line) > 3 means all the RGB values are in same line
if(strlen(line) > 3) {
char *val1 = strtok(line, " ");
char *val2 = strtok(NULL, " ");
char *val3 = strtok(NULL, " ");
// pixelsCounter = 0 means it's the first element.
if(pixelsCounter != 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(val1);
pic->pixelValues[pixelsCounter]->g = atoi(val2);
pic->pixelValues[pixelsCounter]->b = atoi(val3);
pixelsCounter++;
} else if(strlen(line) <= 3) {
/*
* If each individual RGB values are in a separete lines, we will
* use a switch case and a line counter to keep track of where the
* values were inserted and when to know when we got RGB values for
* one pixel
*/
if(pixelsCounter != 0 && lineCounter == 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
switch(lineCounter) {
case 0 :
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(line);
lineCounter++;
continue;
case 1 :
pic->pixelValues[pixelsCounter]->g = atoi(line);
lineCounter++;
continue;
case 2 :
pic->pixelValues[pixelsCounter]->b = atoi(line);
lineCounter=0;
pixelsCounter++;
continue;
default:
continue;
}
}
}
}
pic->pixelValues[pixelsCounter] = NULL;
fclose(f);
return pic;
}
void showPPM(PPM * im) {
printf("%s\n",im->format);
int k = 0;
while(k < im->commentCounter) {
printf("%s\n", im->comments[k]);
k++;
}
printf("%d %d\n", im->width, im->height);
printf("%d\n",im->maxColors);
int j = 0;
while(im->pixelValues[j] != NULL) {
printf("%d %d %d\n", im->pixelValues[j]->r, im->pixelValues[j]->g, im->pixelValues[j]->b);
j++;
}
}
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret) {
int *binaryMessage = decimalToBinary(message, mSize);
int i, j = 0, lineCounter = 0;
for(i = 0; i < 40; i++) {
switch(lineCounter) {
case 0 :
im->pixelValues[j]->r |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 1 :
im->pixelValues[j]->g |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 2 :
im->pixelValues[j]->b |= binaryMessage[i] << 0;
lineCounter=0;
j++;
continue;
default:
continue;
}
}
free(binaryMessage);
return im;
}
/*
* Converts a string into binary to be used in encode function. It
* first converts each letter of the string into ascii code. Then
* finds and stores each of the 8 bits of that int (ascii code of
* the letter) sequentially in an array.
*/
static int *decimalToBinary(const char *message, unsigned int length) {
/*
* malloc is used here instead of [] notation to allocate memory,
* because defining the variable with [] will make its scope
* limited to this function only. Since we want to access this
* array later on, we use malloc to assign space in the memory
* for it so we can access it using a pointer later on.
*/
int k = 0, i, j;
unsigned int c;
unsigned int *binary = malloc(8 * length * sizeof(int));
for(i = 0; i < length; i++) {
c = message[i];
for(j = 7; j >= 0; j--,k++) {
/*
* We check here if the jth bit of the number is 1 or 0
* using the bit operator &. If it is 1, it will return
* 1 because 1 & 1 will be true. Otherwise 0.
*/
if((c >> j) & 1)
binary[k] = 1;
else
binary[k] = 0;
}
}
return binary;
}
关于C 结构值重置为 NULL，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54854415/