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如何在C语言中获取网站图片的尺寸？

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行业动态
2025-01-25
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### 获取网站图片尺寸的多种方法及注意事项

在C语言中获取网站图片的尺寸，通常需要借助网络编程和图像处理相关的库，以下是一个较为详细的步骤说明，包括使用libcurl库进行HTTP请求和使用libjpeg或类似库解析JPEG图片以获取其尺寸。

安装必要的库

确保你的系统上安装了libcurl和libjpeg库，这些库可以通过包管理器安装，例如在Ubuntu上可以使用以下命令：

sudo apt-get install libcurl4-openssl-dev libjpeg-dev

使用libcurl下载图片

libcurl是一个强大的开源库，用于传输数据，你可以使用它来发送HTTP请求并下载图片，以下是一个简单的示例代码，展示如何使用libcurl下载图片到本地文件：

如何在C语言中获取网站图片的尺寸？

#include <stdio.h>
#include <curl/curl.h>
size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
    size_t written = fwrite(ptr, size, nmemb, stream);
    return written;
}
int main() {
    CURL *curl;
    FILE *fp;
    CURLcode res;
    char *url = "https://example.com/image.jpg";
    char outfilename[FILENAME_MAX] = "output.jpg";
    curl = curl_easy_init();
    if (curl) {
        fp = fopen(outfilename,"wb");
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
        fclose(fp);
        if (res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() failed: %s
", curl_easy_strerror(res));
        } else {
            printf("File downloaded successfully.
");
        }
    }
    return 0;
}

使用libjpeg获取图片尺寸

一旦图片被下载到本地文件，你可以使用libjpeg库来读取图片并获取其尺寸，以下是一个示例代码，展示如何读取JPEG图片并获取其宽度和高度：

#include <stdio.h>
#include <jpeglib.h>
#include <setjmp.h>
struct my_error_mgr {
    struct jpeg_error_mgr pub;
    jmp_buf setjmp_buffer;
};
typedef struct my_error_mgr * my_error_ptr;
METHODDEF(void) my_error_exit (j_common_ptr cinfo) {
    my_error_ptr myerr = (my_error_ptr) cinfo->err;
    (*cinfo->err->output_message) (cinfo);
    longjmp(myerr->setjmp_buffer, 1);
}
int get_jpeg_dimensions(const char *filename, int *width, int *height) {
    struct jpeg_decompress_struct cinfo;
    struct my_error_mgr jerr;
    FILE *infile;
    JSAMPARRAY buffer;
    int row_stride;
    if ((infile = fopen(filename, "rb")) == NULL) {
        fprintf(stderr, "can't open %s
", filename);
        return -1;
    }
    cinfo.err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = my_error_exit;
    if (setjmp(jerr.setjmp_buffer)) {
        jpeg_destroy_decompress(&cinfo);
        fclose(infile);
        return -1;
    }
    jpeg_create_decompress(&cinfo);
    jpeg_stdio_src(&cinfo, infile);
    jpeg_read_header(&cinfo, TRUE);
    jpeg_start_decompress(&cinfo);
    row_stride = cinfo.output_width * cinfo.output_components;
    buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
    *width = cinfo.output_width;
    *height = cinfo.output_height;
    jpeg_finish_decompress(&cinfo);
    jpeg_destroy_decompress(&cinfo);
    fclose(infile);
    return 0;
}
int main() {
    int width, height;
    char *filename = "output.jpg";
    if (get_jpeg_dimensions(filename, &width, &height) == 0) {
        printf("Image dimensions: %d x %d
", width, height);
    } else {
        fprintf(stderr, "Failed to get image dimensions.
");
    }
    return 0;
}

综合示例

将上述两个部分结合起来，可以实现一个完整的程序，从网站下载图片并获取其尺寸：

#include <stdio.h>
#include <curl/curl.h>
#include <jpeglib.h>
#include <setjmp.h>
// ... (省略重复的代码) ...
int get_jpeg_dimensions(const char *filename, int *width, int *height); // 声明函数原型
int main() {
    CURL *curl;
    FILE *fp;
    CURLcode res;
    char *url = "https://example.com/image.jpg";
    char outfilename[FILENAME_MAX] = "output.jpg";
    int width, height;
    curl = curl_easy_init();
    if (curl) {
        fp = fopen(outfilename, "wb");
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
        fclose(fp);
        if (res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() failed: %s
", curl_easy_strerror(res));
            return 1;
        } else {
            printf("File downloaded successfully.
");
        }
    } else {
        fprintf(stderr, "Failed to initialize CURL.
");
        return 1;
    }
    if (get_jpeg_dimensions(outfilename, &width, &height) == 0) {
        printf("Image dimensions: %d x %d
", width, height);
    } else {
        fprintf(stderr, "Failed to get image dimensions.
");
        return 1;
    }
    return 0;
}