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【C】获取图片文件格式方法
作者:wqOoops / 发布于2013/5/28/ 628
根据图片文件名和图片文件头标识判断图片格式.

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

	#define EFFECTIVELEN 10
	#define GETBYTELEN 2

	/*---JPEG/JPG(1)---*/
	#define IMAGE_JPEG_JPG "JPEG/JPG"
	#define JPEG_FIRSTBIT "FF"
	#define JPEG_SECONDBIT "D8"

	/*---BMP(2)---*/
	#define IMAGE_BMP "BMP"
	#define BMP_FIRSTBIT "42"
	#define BMP_SECONDBIT "4D"

	/*---PNG(3)---*/
	#define IMAGE_PNG "PNG"
	#define PNG_FIRSTBIT "89"
	#define PNG_SECONDBIT "50"

	/*---GIF(4)---*/
	#define IMAGE_GIF "GIF"
	#define GIF_FIRSTBIT "47"
	#define GIF_SECONDBIT "49"
	#define GIF_THIRDBIT "46"
	#define GIF_FIFTHBIT1 "39" // 可能存在是37
	#define GIF_FIFTHBIT2 "37"

	/*---TIFF(5)---*/
	#define IMAGE_TIFF "TIFF"
	#define TIFF_FIRSTBIT "4D"
	#define TIFF_SECONDBIT "4D"
	#define TIFF_FIRSTBIT2 "49" // 或者
	#define TIFF_SECONDBIT2 "49"

	/*---ICO(6)---*/
	#define IMAGE_ICO "ICO"
	#define ICO_THIRDBIT "1" // 01
	#define ICO_FIFTHBIT "1" // 01

	/*---TGA(7)---*/
	#define IMAGE_TGA "TGA"
	#define TGA_THIRDBIT "2" // 02
	#define TGA_FIFTHBIT "0" // 00

	/*---CUR(8)---*/
	#define IMAGE_CUR "CUR"
	#define CUR_THIRDBIT "2" // 02
	#define CUR_FIFTHBIT "1" // 01

	/*---PCX(9)---*/
	#define IMAGE_PCX "PCX"
	#define PCX_FIRSTBIT "A" // 0A

	/*---IFF(10)---*/
	#define IMAGE_IFF "IFF"
	#define IFF_FIRSTBIT "46"
	#define IFF_SECONDBIT "4F"
	#define IFF_THIRDBIT "52"
	#define IFF_FORTHBIT "4D"

	/*---ANI(11)---*/
	#define IMAGE_ANI "ANI"
	#define ANI_FIRSTBIT "52"
	#define ANI_SECONDBIT "49"
	#define ANI_THIRDBIT "46"
	#define ANI_FORTHBIT "46"

	char MImagesType[12][10] = {"JPEG","JPG","BMP","PNG","GIF","TIFF","aICO","TGA",
	 "CUR","PCX","IFF","ANI"};
	char LImagesType[12][10] = {"jpeg","jpg","bmp","png","gif","tiff","aico","tga",
	 "cur","pcx","iff","ani"};

	// 反转字符串
	void reserve(char *p, char *q)
	{
	while(p < q){
	 *p ^= *q;
	 *q ^= *p;
	 *p ^= *q;
	 p++;
	 q--;
	}
	}

	char *Check_Image_Header(char *Filename)
	{
	FILE *fd;
	unsigned char *imagebuf;
	int filesize = 0;
	unsigned char firstBit[3];
	unsigned char secondBit[3];
	unsigned char thirdBit[3];
	unsigned char forthBit[3];
	unsigned char fifthBit[3];

	assert(Filename != NULL);

	if( (fd = fopen(Filename, "rb")) == NULL){
	 perror("fopen error\n");
	 exit(1);
	}

	fseek(fd, 0, SEEK_END);
	filesize = ftell(fd); // 返回当前文件位置，也就是说返回FILE指针当前位置。
	rewind(fd); // 将文件内部的位置指针重新指向一个流（数据流/文件）的开头

	imagebuf = (unsigned char *)malloc(EFFECTIVELEN * sizeof(unsigned char) + 1);
	fread(imagebuf, sizeof(unsigned char), EFFECTIVELEN, fd);

	snprintf(firstBit, sizeof(firstBit), "%X", imagebuf[0]);
	snprintf(secondBit, sizeof(secondBit), "%X", imagebuf[1]);
	snprintf(thirdBit, sizeof(thirdBit), "%X", imagebuf[2]);
	snprintf(forthBit, sizeof(forthBit), "%X", imagebuf[3]);
	snprintf(fifthBit, sizeof(fifthBit), "%X", imagebuf[4]);

	if( (0 == strncmp(firstBit, JPEG_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, JPEG_SECONDBIT, GETBYTELEN))) {
	 return IMAGE_JPEG_JPG;
	}
	if( (0 == strncmp(firstBit, BMP_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, BMP_SECONDBIT, GETBYTELEN))) {
	 return IMAGE_BMP;
	}
	if( (0 == strncmp(firstBit, PNG_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, PNG_SECONDBIT, GETBYTELEN))) {
	 return IMAGE_PNG;
	}
	if( (0 == strncmp(firstBit, GIF_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, GIF_SECONDBIT, GETBYTELEN)) &&
	 (0 == strncmp(thirdBit, GIF_THIRDBIT, GETBYTELEN)) &&
	 ((0 == strncmp(fifthBit, GIF_FIFTHBIT1, GETBYTELEN)) ||
	 (0 == strncmp(fifthBit, GIF_FIFTHBIT2, GETBYTELEN)))) {
	 return IMAGE_GIF;
	}
	if( ((0 == strncmp(firstBit, TIFF_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, TIFF_SECONDBIT, GETBYTELEN))) ||
	 ((0 == strncmp(firstBit, TIFF_FIRSTBIT2, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, TIFF_SECONDBIT2, GETBYTELEN)))) {
	 return IMAGE_TIFF;
	}
	if( (0 == strncmp(thirdBit, ICO_THIRDBIT, GETBYTELEN)) &&
	 (0 == strncmp(fifthBit, ICO_FIFTHBIT, GETBYTELEN))){
	 return IMAGE_ICO;
	}
	if( (0 == strncmp(thirdBit, TGA_THIRDBIT, GETBYTELEN)) &&
	 (0 == strncmp(fifthBit, TGA_FIFTHBIT, GETBYTELEN))){
	 return IMAGE_TGA;
	}
	if( (0 == strncmp(thirdBit, CUR_THIRDBIT, GETBYTELEN)) &&
	 (0 == strncmp(fifthBit, CUR_FIFTHBIT, GETBYTELEN))){
	 return IMAGE_CUR;
	}
	if(0 == strncmp(firstBit, PCX_FIRSTBIT, GETBYTELEN)){
	 return IMAGE_PCX;
	}
	if( (0 == strncmp(firstBit, IFF_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, IFF_SECONDBIT, GETBYTELEN)) &&
	 (0 == strncmp(thirdBit, IFF_THIRDBIT, GETBYTELEN)) &&
	 (0 == strncmp(forthBit, IFF_FORTHBIT, GETBYTELEN))) {
	 return IMAGE_IFF;
	}
	if( (0 == strncmp(firstBit, ANI_FIRSTBIT, GETBYTELEN)) &&
	 (0 == strncmp(secondBit, ANI_SECONDBIT, GETBYTELEN)) &&
	 (0 == strncmp(thirdBit, ANI_THIRDBIT, GETBYTELEN)) &&
	 (0 == strncmp(forthBit, ANI_FORTHBIT, GETBYTELEN))) {
	 return IMAGE_ANI;
	}

	free(imagebuf);
	imagebuf = NULL;
	fclose(fd);
	return NULL;
	}

	char *Get_image_type(char *Filename)
	{
	assert(Filename != NULL);

	char *TypeName;
	char *pStart = NULL;
	char *pEnd = NULL;
	char *name;
	int i = 0;

	name = (char *)malloc(strlen(Filename) + 1);
	memset(name, 0, sizeof(name));
	strcpy(name, Filename);
	pStart = name;
	pEnd = pStart + strlen(name) - 1;
	reserve(pStart, pEnd);

	TypeName = (char *)malloc(strlen(name) + 1);
	memset(TypeName, 0, sizeof(TypeName));
	sscanf(name, "%[^.]", TypeName); // 取&ldquo;.&rdquo;前面的部分
	pStart = TypeName;
	pEnd = pStart + strlen(TypeName) - 1;
	reserve(pStart, pEnd);
	
	for(i=0; i<12; i++){
	#if 0
	 // 只匹配部分字符串，导致判断出错。
	 if( (0 == strncmp(TypeName, MImagesType[i], strlen(MImagesType[i]))) ||
	 (0 == strncmp(TypeName, LImagesType[i], strlen(LImagesType[i]))))
	 return MImagesType[i];
	#endif
	 if( (0 == strcmp(TypeName, MImagesType[i])) || (0 == strcmp(TypeName, LImagesType[i])))
	 return MImagesType[i];
	}

	free(name);
	free(TypeName);
	name = NULL;
	TypeName = NULL;
	
	return Check_Image_Header(Filename);
	}

	int main(int argc, char *argv[])
	{
	int res = -1;
	char *imageType;

	if(argc < 2){
	 printf("usage: %s <imagefilename>\n", argv[0]);
	 exit(1);
	}

	imageType = Get_image_type(argv[1]);

	if(!imageType)
	 printf("not a picture!\n");
	else
	 printf("%s\n", imageType);

	return 0;
	}
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