pure C read write bmp file

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

int getWH(int *w, int *h, const char *fileName)
{

char bmpName[128];									// bmp file name
FILE *fp=NULL;											// FILE pointer
unsigned char header[54];						// for bmp header look ahead
int temp=0, width = 0, height = 0 ;		// local variable for calculation
int i = 0;															// loop variable
sprintf(bmpName,"%s.bmp",fileName);// 24bit bit map 未使用調色盤

if(  !(fp = fopen(bmpName,"rb") ) )
return -1;

fread( header, sizeof(unsigned char), 54, fp);	// read bmp header into header[54]

for( i = 0 ; i != 4 ; ++i )											// get width from byte 18 ~ byte 22 in header[54]
{
temp = (long)header[18+i];
temp = temp <<( 8*i );
width += temp;
}
for( i = 0 ; i != 4 ; ++i )											// get width from byte 22 ~ byte 26 in header[54]
{
temp = (long)header[22+i];
temp = temp <<( 8*i );
height += temp;
}
*w = width;
*h = height;

fclose(fp);

return 0;
}//end if getWT

int bmp_read( unsigned char *image, int xSize, int ySize, const char *fileName )
{
char fnameBmp[128]={0};
FILE *fp=NULL;
unsigned char header[54]={0};	// for bmp header

sprintf( fnameBmp,"%s.bmp",fileName);

if(  !(fp = fopen(fnameBmp,"rb") ) )
return -1;

fread( header, sizeof(unsigned char), 54, fp);	// read bmp header into header[54], based on byte
fread( image, sizeof(unsigned char), (size_t)(long)xSize * ySize * 3, fp);	// read image array, based on byte

fclose(fp);
return 0;
}//end of function bmp read

int bmp_write( unsigned char* image, int xSize, int ySize, char *fileName)
{
unsigned char header[54]={
0x42,0x4d, 0, 0,   0,  0,  0,  0, 0 , 0,        // 0~1 st byte : 'BM'
54,       0, 0, 0, 40,  0,  0,  0, 0 , 0,		// 10th byte : offset = 54 = header size
0,       0, 0, 0,   0,  0,  1,  0,24, 0,		// 26th byte : 圖層數，28th byte : 24 bit 點陣圖
0,       0, 0, 0,   0,  0,  0,  0,   0, 0,
0,       0, 0, 0,   0,   0,  0, 0,   0, 0,
0,       0, 0, 0
};

// sizeof(long) = 4
long fileSize = (long)xSize * (long)ySize * 3 +54 ;		// image array size + 54
long temp = 0;							// temp for byte convertion
long width = xSize;					// image width
long height = ySize;				// image height
char bmpName[128]={0};    // filename
int i = 0;										// loop variable

FILE *fp;

for( i=0 ; i != 4 ; ++i)				// write fileSize from byte2 ~ byte 6
{
header[2+i] = (unsigned char)( fileSize >> (8*i) ) & 0x000000ff;
}
for( i=0 ; i != 4 ; ++i)				// write width from byte18 ~ byte 22
{
header[18+i] = (unsigned char)( width >> (8*i) ) & 0x000000ff;
}
for( i=0 ; i != 4 ; ++i)				// write height from byte22 ~ byte 26
{
header[22+i] = (unsigned char)( height >> (8*i) ) & 0x000000ff;
}

sprintf(bmpName,"%s.bmp",fileName);

if( ! ( fp = fopen(bmpName,"wb")  ) )									// 檔案名稱
return -1;

fwrite(header, sizeof(unsigned char), 54, fp);												// write header
fwrite(image, sizeof(unsigned char),(size_t)(long)xSize*ySize*3, fp);		// write image array

fclose(fp);
return 0;
}//end of function bmp_write

int main()
{

unsigned char *image=NULL;
int xSize = 0;
int ySize = 0;
char fileName[128]={0};
printf("Please input the filename to load\n");
scanf("%s",fileName);
getWH(&xSize, &ySize, fileName);					// get image size by calling getWH

image = (unsigned char*)malloc( (size_t) xSize * ySize * 3 );

if( image == NULL )												// if fail to open file
return -1;

bmp_read( image, xSize, ySize, fileName);

strcat(fileName," copy");									// change file name with copy postfix
bmp_write(image,xSize, ySize,fileName);		// write to outpit file

free(image);															// relese 2D image array

return 0;
}//end of main