C语言实现修改文件中指定字符串哪一行内容

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

/*参数： filepath - 要修改的文件   str - 修改为的字符串 */
void ModifyFile(char* filepath, char *str)
{
 
	char linebuffer[512] = {0};
	char buffer1[512] = {0};
	char buffer2[512] = {0};
	//char buf[512] = {0}; 
	char cmd[256] = "rm temp.txt";

	FILE *fp     = fopen(filepath, "r");
	FILE *fpttmp = fopen("temp.txt", "wt+");
 
	while(fgets(linebuffer, 512, fp))
	{
		sscanf(linebuffer, "%[^_]_%[^_]", buffer1,buffer2);
		if(!strcmp("11", buffer1))
		{
			memset(linebuffer, '\0', strlen(linebuffer)+1);
			memcpy(linebuffer, str, strlen(str)+1);
			//linebuffer[7]  = '\0';
			fprintf(fpttmp, "%s", linebuffer); 
			fprintf(fpttmp,"\n");
		}
		else
		{
			fprintf(fpttmp, "%s", linebuffer); 
		}
   }
	fclose(fp);
	fclose(fpttmp);

	//清空文件中的内容
	fp	 = fopen(filepath, "w");
	fclose(fp);

	fp     = fopen(filepath, "wt+");
	fpttmp = fopen("temp.txt", "r");
 
	while(fgets(linebuffer, 512, fpttmp))
	{
		
		fprintf(fp, "%s", linebuffer); 
   	}
	fclose(fp);
	fclose(fpttmp);
	system(cmd);
	
}


int main()
{ 
	char name[128] = "wugaoquan";
	ModifyFile("mm.txt", name);  
	
	return 0;
}