使用struct变量和struct数组读取bmp图像的代码 . 请建议我对malloc进行类型转换的正确方法(代码下面列出的错误):
#include<stdio.h>
#include<stdlib.h>
typedef struct bands{
/* .bmp image store pixel colors in "bgr" sequence */
unsigned char b,g,r; //in 24bit bmp, we need to use 8bit datatype for each color
}bands;
int main()
{
FILE *bmpimage; //ptr to read image file
FILE *redpix,*greenpix,*bluepix; //ptr to create band/color wise file
unsigned short pix_x=223,pix_y=197; /*pix_x: no. of pixels in a row, pix_y: no. of pixels in a column of input image*/
unsigned short n_pix=pix_x*pix_y; /*variable to count total no. of pixels*/
bmpimage=fopen("blocks223x197.bmp","r"); //24 bit bmpimage
redpix=fopen("redpixels.txt","w");
greenpix=fopen("greenpixels.txt","w");
bluepix=fopen("bluepixels.txt","w");
/* Define a pointer to a memory block,'*readbuffer',
that has 'n_pix' no. of memory blocks each of size same as struct bands */
bands *readbuffer=(char*)malloc(n_pix*sizeof(*readbuffer));
int n;
//Create memory for each of 'n_pix' no. of pixel array of each color
for(n=0;n<n_pix;n++){
unsigned char *readbuffer[n].b = (char*) malloc(sizeof(readbuffer[n].b));
unsigned char *readbuffer[n].g = (char*) malloc(sizeof(readbuffer[n].g));
unsigned char *readbuffer[n].r = (char*) malloc(sizeof(readbuffer[n].r));
}
if(!bmpimage){printf("Error reading bmpimage!");return 1;}
if(readbuffer==NULL){printf("NULL buffer"); exit(1);}
/* Go to 54th byte to access pixelvalue data (since, 24bit bmp format) */
fseek(bmpimage,54,SEEK_SET);
/* Read 'n_pix' no. of 'bgr' blocks each of which are of the size same as "struct bands" */
fread(readbuffer,sizeof(bands),n_pix,bmpimage); /*read 'n_pix' no. of 'bgr' blocks each of which are of the size same as "struct bands" to the memory address, 'readbuffer' or '&readbuffer[0]' */
int n_blocks=(sizeof(readbuffer)/sizeof(bands));
printf("no. of blocks read= %d, n_pix=%d",n_blocks,n_pix);
int i,j; int count; count=0;
/* logic to print pixel values in correct order*/
for(i=pix_y;i>0;i--){ /*for accessing row data. Choose to print from bottom to top*/
for(j=1;j<=pix_x;j++){ /*for accessing column data. Print from left to right*/
if(j!=pix_x){
fprintf(redpix,"%d,",readbuffer[(i-1)*pix_x + j].r);
fprintf(greenpix,"%d,",readbuffer[(i-1)*pix_x + j].g);
fprintf(bluepix,"%d,",readbuffer[(i-1)*pix_x + j].b);
}
else{
count++;
fprintf(redpix,"%d\n",readbuffer[(i-1)*pix_x + j].r);
fprintf(greenpix,"%d\n",readbuffer[(i-1)*pix_x + j].g);
fprintf(bluepix,"%d\n",readbuffer[(i-1)*pix_x + j].b);
}
}
}
// free allocated memory
for(n=0;n<n_pix;n++){
free(readbuffer[n].b) ;
free(readbuffer[n].g) ;
free(readbuffer[n].r) ;
}
fclose(bmpimage);fclose(redpix);fclose(bluepix);fclose(greenpix);
return 0;
}
参考文献:How to properly malloc for array of struct in C
malloc an array of struct pointers vs array of structs
错误列表:
bmpread_check.c:在函数'main'中:bmpread_check.c:24:19:警告:从不兼容的指针类型初始化> [默认启用] band readbuffer =(char)malloc(n_pix * sizeof(* readbuffer)); ^ bmpread_check.c:29:33:错误:在' . '之前预期'=',',',';','asm'或'attribute'> token unsigned char readbuffer [n] .b =(char)malloc(sizeof(readbuffer [n] .b)); ^ bmpread_check.c:29:33:错误:' . '之前的预期表达式token bmpread_check.c:30:33:error:在' . '之前预期'=',',',';','asm'或'attribute'> token unsigned char readbuffer [n] .g =(char)malloc(sizeof(readbuffer [n] .g)); ^ bmpread_check.c:30:33:错误:' . '之前的预期表达式token bmpread_check.c:31:33:error:在' . '之前预期'=',',',';','asm'或'attribute'> token unsigned char readbuffer [n] .r =(char)malloc(sizeof(readbuffer [n] .r)); ^ bmpread_check.c:31:33:错误:' . '之前的预期表达式token bmpread_check.c:69:5:警告:传递'free'的参数1使得指针来自>整数而没有强制转换[默认启用] free(readbuffer [n] .b); ^在bmpread_check.c中包含的文件中:3:0:c:\ mingw \ include \ stdlib.h:357:38:注意:预期'void'但参数是>类型'unsigned char'_CRTIMP void __cdecl __MINGW_NOTHROW free(无效); ^ bmpread_check.c:70:5:警告:传递'free'的参数1使得指针来自>整数而没有强制转换[默认启用] free(readbuffer [n] .g); ^在bmpread_check.c中包含的文件中:3:0:c:\ mingw \ include \ stdlib.h:357:38:注意:预期'void'但参数是>类型'unsigned char'_CRTIMP void __cdecl __MINGW_NOTHROW free(无效); ^ bmpread_check.c:71:5:警告:传递'free'的参数1使得指针来自>整数而没有强制转换[默认启用] free(readbuffer [n] .r); ^在bmpread_check.c中包含的文件中:3:0:c:\ mingw \ include \ stdlib.h:357:38:注意:预期'void'但参数类型>'unsigned char'_CRTIMP void __cdecl __MINGW_NOTHROW free(无效); ^
2 回答
这个:
(注意:不是
*readbuffer
. 这是bands
)已经为所有
n_pix
频段分配了内存 .没有必要为
b, g, r
分配内存,因为它们不是指针 .所以,
不需要 .
变量
b
,g
&r
不是指针,而是无符号的8位变量 . 因此,为这种情况分配内存的正确方法是分配一个具有总像素数的结构的数组,即宽度乘以图像的高度 .这可以通过动态分配结构指针
bands*
来实现,如下所示 .bands *readbuffer = malloc(n_pix * sizeof(bands));
该规则将分配结构n_pix次,以便您可以在每个像素位置初始化和访问像素值
b
,g
&r
,如下所示 .i
可以是0
到n_pix-1
的任何内容